Method and apparatus for intra block copy mode coding with search range switching

ABSTRACT

This disclosure relates generally to video coding and particularly to intra block copy coding mode. For example, a method is disclosed for reconstructing a video block in a video stream. The method may include extracting at least one syntax element from the video stream, the at least one syntax element being associated with an intra block copy (IBC) prediction of the video block; determining an IBC referencing mode for the IBC prediction of the video block, the IBC referencing mode comprises one of no-IBC mode, a local-referencing IBC mode, a non-local-referencing IBC mode, and a local-and-non-local-referencing IBC mode; and generating reconstructed samples of the video block from the video stream based on the IBC referencing mode.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority to U.S.Provisional Application No. 63/245,665, entitle “Method and Apparatusfor Intra Block Copy (IntraBC) Mode Coding with Search Range Switching”,filed on Sep. 17, 2021, which is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

This disclosure relates generally to video coding and particularly tointra block copy coding mode.

BACKGROUND

This background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing of thisapplication, are neither expressly nor impliedly admitted as prior artagainst the present disclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, with each picture having a spatialdimension of, for example, 1920×1080 luminance samples and associatedfull or subsampled chrominance samples. The series of pictures can havea fixed or variable picture rate (alternatively referred to as framerate) of, for example, 60 pictures per second or 60 frames per second.Uncompressed video has specific bitrate requirements for streaming ordata processing. For example, video with a pixel resolution of1920×1080, a frame rate of 60 frames/second, and a chroma subsampling of4:2:0 at 8 bit per pixel per color channel requires close to 1.5 Gbit/sbandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the uncompressed input video signal, through compression.Compression can help reduce the aforementioned bandwidth and/or storagespace requirements, in some cases, by two orders of magnitude or more.Both lossless compression and lossy compression, as well as acombination thereof can be employed. Lossless compression refers totechniques where an exact copy of the original signal can bereconstructed from the compressed original signal via a decodingprocess. Lossy compression refers to coding/decoding process whereoriginal video information is not fully retained during coding and notfully recoverable during decoding. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is made smallenough to render the reconstructed signal useful for the intendedapplication albeit some information loss. In the case of video, lossycompression is widely employed in many applications. The amount oftolerable distortion depends on the application. For example, users ofcertain consumer video streaming applications may tolerate higherdistortion than users of cinematic or television broadcastingapplications. The compression ratio achievable by a particular codingalgorithm can be selected or adjusted to reflect various distortiontolerance: higher tolerable distortion generally allows for codingalgorithms that yield higher losses and higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories and steps, including, for example, motion compensation,Fourier transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, a picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be referred to as an intra picture. Intra pictures and theirderivatives such as independent decoder refresh pictures, can be used toreset the decoder state and can, therefore, be used as the first picturein a coded video bitstream and a video session, or as a still image. Thesamples of a block after intra prediction can then be subject to atransform into frequency domain, and the transform coefficients sogenerated can be quantized before entropy coding. Intra predictionrepresents a technique that minimizes sample values in the pre-transformdomain. In some cases, the smaller the DC value after a transform is,and the smaller the AC coefficients are, the fewer the bits that arerequired at a given quantization step size to represent the block afterentropy coding.

Traditional intra coding such as that known from, for example, MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt coding/decoding of blocks based on, for example, surroundingsample data and/or metadata that are obtained during the encoding and/ordecoding of spatially neighboring, and that precede in decoding orderthe blocks of data being intra coded or decoded. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction uses reference data only from the currentpicture under reconstruction and not from other reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques are available in a given video coding technology,the technique in use can be referred to as an intra prediction mode. Oneor more intra prediction modes may be provided in a particular codec. Incertain cases, modes can have submodes and/or may be associated withvarious parameters, and mode/submode information and intra codingparameters for blocks of video can be coded individually or collectivelyincluded in mode codewords. Which codeword to use for a given mode,submode, and/or parameter combination can have an impact in the codingefficiency gain through intra prediction, and so can the entropy codingtechnology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). Generally, for intra prediction, a predictor block can be formedusing neighboring sample values that have become available. For example,available values of particular set of neighboring samples along certaindirection and/or lines may be copied into the predictor block. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions specified in H.265's 33 possible intra predictordirections (corresponding to the 33 angular modes of the 35 intra modesspecified in H.265). The point where the arrows converge (101)represents the sample being predicted. The arrows represent thedirection from which neighboring samples are used to predict the sampleat 101. For example, arrow (102) indicates that sample (101) ispredicted from a neighboring sample or samples to the upper right, at a45 degree angle from the horizontal direction. Similarly, arrow (103)indicates that sample (101) is predicted from a neighboring sample orsamples to the lower left of sample (101), in a 22.5 degree angle fromthe horizontal direction.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are example referencesamples that follow a similar numbering scheme. A reference sample islabelled with an R, its Y position (e.g., row index) and X position(column index) relative to block (104). In both H.264 and H.265,prediction samples adjacently neighboring the block under reconstructionare used.

Intra picture prediction of block 104 may begin by copying referencesample values from the neighboring samples according to a signaledprediction direction. For example, assuming that the coded videobitstream includes signaling that, for this block 104, indicates aprediction direction of arrow (102)—that is, samples are predicted froma prediction sample or samples to the upper right, at a 45-degree anglefrom the horizontal direction. In such a case, samples S41, S32, S23,and S14 are predicted from the same reference sample R05. Sample S44 isthen predicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has continued to develop. In H.264 (year 2003), for example,nine different direction are available for intra prediction. Thatincreased to 33 in H.265 (year 2013), and JEM/VVC/BMS, at the time ofthis disclosure, can support up to 65 directions. Experimental studieshave been conducted to help identify the most suitable intra predictiondirections, and certain techniques in the entropy coding may be used toencode those most suitable directions in a small number of bits,accepting a certain bit penalty for directions. Further, the directionsthemselves can sometimes be predicted from neighboring directions usedin the intra prediction of the neighboring blocks that have beendecoded.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions in various encoding technologies developed overtime.

The manner for mapping of bits representing intra prediction directionsto the prediction directions in the coded video bitstream may vary fromvideo coding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions for intro prediction that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well-designed videocoding technology, may be represented by a larger number of bits thanmore likely directions.

Inter picture prediction, or inter prediction may be based on motioncompensation. In motion compensation, sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), may be used for a prediction of a newly reconstructedpicture or picture part (e.g., a block). In some cases, the referencepicture can be the same as the picture currently under reconstruction.MVs may have two dimensions X and Y, or three dimensions, with the thirddimension being an indication of the reference picture in use (akin to atime dimension).

In some video compression techniques, a current MV applicable to acertain area of sample data can be predicted from other MVs, for examplefrom those other MVs that are related to other areas of the sample datathat are spatially adjacent to the area under reconstruction and precedethe current MV in decoding order. Doing so can substantially reduce theoverall amount of data required for coding the MVs by relying onremoving redundancy in correlated MVs, thereby increasing compressionefficiency. MV prediction can work effectively, for example, becausewhen coding an input video signal derived from a camera (known asnatural video) there is a statistical likelihood that areas larger thanthe area to which a single MV is applicable move in a similar directionin the video sequence and, therefore, can in some cases be predictedusing a similar motion vector derived from MVs of neighboring area. Thatresults in the actual MV for a given area to be similar or identical tothe MV predicted from the surrounding MVs. Such an MV in turn may berepresented, after entropy coding, in a smaller number of bits than whatwould be used if the MV is coded directly rather than predicted from theneighboring MV(s). In some cases, MV prediction can be an example oflossless compression of a signal (namely: the MVs) derived from theoriginal signal (namely: the sample stream). In other cases, MVprediction itself can be lossy, for example because of rounding errorswhen calculating a predictor from several surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 specifies, described below is atechnique henceforth referred to as “spatial merge”.

Specifically, referring to FIG. 2 , a current block (201) comprisessamples that have been found by the encoder during the motion searchprocess to be predictable from a previous block of the same size thathas been spatially shifted. Instead of coding that MV directly, the MVcan be derived from metadata associated with one or more referencepictures, for example from the most recent (in decoding order) referencepicture, using the MV associated with either one of five surroundingsamples, denoted A0, A1, and B0, B1, B2 (202 through 206, respectively).In H.265, the MV prediction can use predictors from the same referencepicture that the neighboring block uses.

SUMMARY

Aspects of the disclosure relates generally to video coding andparticularly to intra block copy coding mode. In some exampleimplementations, TBD.

Aspects of the disclosure also provide a video encoding or decodingdevice or apparatus including a circuitry configured to carry out any ofthe method implementations above.

Aspects of the disclosure also provide non-transitory computer-readablemediums storing instructions which when executed by a computer for videodecoding and/or encoding cause the computer to perform the methods forvideo decoding and/or encoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A shows a schematic illustration of an exemplary subset of intraprediction directional modes;

FIG. 1B shows an illustration of exemplary intra prediction directions;

FIG. 2 shows a schematic illustration of a current block and itssurrounding spatial merge candidates for motion vector prediction in oneexample;

FIG. 3 shows a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an example embodiment;

FIG. 4 shows a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an example embodiment;

FIG. 5 shows a schematic illustration of a simplified block diagram of avideo decoder in accordance with an example embodiment;

FIG. 6 shows a schematic illustration of a simplified block diagram of avideo encoder in accordance with an example embodiment;

FIG. 7 shows a block diagram of a video encoder in accordance withanother example embodiment;

FIG. 8 shows a block diagram of a video decoder in accordance withanother example embodiment;

FIG. 9 shows a scheme of coding block partitioning according to exampleembodiments of the disclosure;

FIG. 10 shows another scheme of coding block partitioning according toexample embodiments of the disclosure;

FIG. 11 shows another scheme of coding block partitioning according toexample embodiments of the disclosure;

FIG. 12 shows an example partitioning of a base block into coding blocksaccording to an example partitioning scheme;

FIG. 13 shows an example ternary partitioning scheme;

FIG. 14 shows an example quadtree binary tree coding block partitioningscheme;

FIG. 15 shows a scheme for partitioning a coding block into multipletransform blocks and coding order of the transform blocks according toexample embodiments of the disclosure;

FIG. 16 shows another scheme for partitioning a coding block intomultiple transform blocks and coding order of the transform blockaccording to example embodiments of the disclosure;

FIG. 17 shows another scheme for partitioning a coding block intomultiple transform blocks according to example embodiments of thedisclosure;

FIG. 18 illustrates concept of Intra Block Copy (IBC) usingreconstructed coding block in a same frame to predict a current codingblock;

FIG. 19 illustrates example reconstructed sample that are available asreference samples for IBC;

FIG. 20 illustrates example reconstructed sample that are available asreference samples for IBC with some example restrictions;

FIG. 21 illustrates an example on-chip Reference Sample Memory (RSM)updating mechanism for IBC;

FIG. 22 illustrates a spatial view of the example on-chip RSM updatingmechanism of FIG. 21 ;

FIG. 23 illustrates another example on-chip Reference Sample Memory(RSM) updating mechanism for IBC;

FIG. 24 illustrates a comparison of spatial views of an example RSMupdating mechanism for IBC for horizontally split super block andvertically split super block;

FIG. 25 illustrates example non-local and local search areas for IBCreference blocks;

FIG. 26 illustrates an example restriction of location of referenceblock for IBC employing both local and non-local reference block searchareas;

FIG. 27 shows a flow chart of method according to an example embodimentof the disclosure; and

FIG. 28 shows a schematic illustration of a computer system inaccordance with example embodiments of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention will now be described in detail hereinafter with referenceto the accompanied drawings, which form a part of the present invention,and which show, by way of illustration, specific examples ofembodiments. Please note that the invention may, however, be embodied ina variety of different forms and, therefore, the covered or claimedsubject matter is intended to be construed as not being limited to anyof the embodiments to be set forth below. Please also note that theinvention may be embodied as methods, devices, components, or systems.Accordingly, embodiments of the invention may, for example, take theform of hardware, software, firmware or any combination thereof.

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning. Thephrase “in one embodiment” or “in some embodiments” as used herein doesnot necessarily refer to the same embodiment and the phrase “in anotherembodiment” or “in other embodiments” as used herein does notnecessarily refer to a different embodiment. Likewise, the phrase “inone implementation” or “in some implementations” as used herein does notnecessarily refer to the same implementation and the phrase “in anotherimplementation” or “in other implementations” as used herein does notnecessarily refer to a different implementation. It is intended, forexample, that claimed subject matter includes combinations of exemplaryembodiments/implementations in whole or in part.

In general, terminology may be understood at least in part from usage incontext. For example, terms, such as “and”, “or”, or “and/or,” as usedherein may include a variety of meanings that may depend at least inpart upon the context in which such terms are used. Typically, “or” ifused to associate a list, such as A, B or C, is intended to mean A, B,and C, here used in the inclusive sense, as well as A, B or C, here usedin the exclusive sense. In addition, the term “one or more” or “at leastone” as used herein, depending at least in part upon context, may beused to describe any feature, structure, or characteristic in a singularsense or may be used to describe combinations of features, structures orcharacteristics in a plural sense. Similarly, terms, such as “a”, “an”,or “the”, again, may be understood to convey a singular usage or toconvey a plural usage, depending at least in part upon context. Inaddition, the term “based on” or “determined by” may be understood asnot necessarily intended to convey an exclusive set of factors and may,instead, allow for existence of additional factors not necessarilyexpressly described, again, depending at least in part on context.

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the example of FIG. 3 , the first pair of terminal devices (310) and(320) may perform unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., of a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display the video pictures according tothe recovered video data. Unidirectional data transmission may beimplemented in media serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data that may be implemented, for example,during a videoconferencing application. For bidirectional transmissionof data, in an example, each terminal device of the terminal devices(330) and (340) may code video data (e.g., of a stream of video picturesthat are captured by the terminal device) for transmission to the otherterminal device of the terminal devices (330) and (340) via the network(350). Each terminal device of the terminal devices (330) and (340) alsomay receive the coded video data transmitted by the other terminaldevice of the terminal devices (330) and (340), and may decode the codedvideo data to recover the video pictures and may display the videopictures at an accessible display device according to the recoveredvideo data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) may be implemented as servers, personal computers and smart phonesbut the applicability of the underlying principles of the presentdisclosure may not be so limited. Embodiments of the present disclosuremay be implemented in desktop computers, laptop computers, tabletcomputers, media players, wearable computers, dedicated videoconferencing equipment, and/or the like. The network (350) representsany number or types of networks that convey coded video data among theterminal devices (310), (320), (330) and (340), including for examplewireline (wired) and/or wireless communication networks. Thecommunication network (350)9 may exchange data in circuit-switched,packet-switched, and/or other types of channels. Representative networksinclude telecommunications networks, local area networks, wide areanetworks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (350) may beimmaterial to the operation of the present disclosure unless explicitlyexplained herein.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, a placement of a video encoder and a video decoder in avideo streaming environment. The disclosed subject matter may be equallyapplicable to other video applications, including, for example, videoconferencing, digital TV broadcasting, gaming, virtual reality, storageof compressed video on digital media including CD, DVD, memory stick andthe like, and so on.

A video streaming system may include a video capture subsystem (413)that can include a video source (401), e.g., a digital camera, forcreating a stream of video pictures or images (402) that areuncompressed. In an example, the stream of video pictures (402) includessamples that are recorded by a digital camera of the video source 401.The stream of video pictures (402), depicted as a bold line to emphasizea high data volume when compared to encoded video data (404) (or codedvideo bitstreams), can be processed by an electronic device (420) thatincludes a video encoder (403) coupled to the video source (401). Thevideo encoder (403) can include hardware, software, or a combinationthereof to enable or implement aspects of the disclosed subject matteras described in more detail below. The encoded video data (404) (orencoded video bitstream (404)), depicted as a thin line to emphasize alower data volume when compared to the stream of uncompressed videopictures (402), can be stored on a streaming server (405) for future useor directly to downstream video devices (not shown). One or morestreaming client subsystems, such as client subsystems (406) and (408)in FIG. 4 can access the streaming server (405) to retrieve copies (407)and (409) of the encoded video data (404). A client subsystem (406) caninclude a video decoder (410), for example, in an electronic device(430). The video decoder (410) decodes the incoming copy (407) of theencoded video data and creates an outgoing stream of video pictures(411) that are uncompressed and that can be rendered on a display (412)(e.g., a display screen) or other rendering devices (not depicted). Thevideo decoder 410 may be configured to perform some or all of thevarious functions described in this disclosure. In some streamingsystems, the encoded video data (404), (407), and (409) (e.g., videobitstreams) can be encoded according to certain video coding/compressionstandards. Examples of those standards include ITU-T RecommendationH.265. In an example, a video coding standard under development isinformally known as Versatile Video Coding (VVC). The disclosed subjectmatter may be used in the context of VVC, and other video codingstandards.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anyembodiment of the present disclosure below. The video decoder (510) canbe included in an electronic device (530). The electronic device (530)can include a receiver (531) (e.g., receiving circuitry). The videodecoder (510) can be used in place of the video decoder (410) in theexample of FIG. 4 .

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In the same or another embodiment,one coded video sequence may be decoded at a time, where the decoding ofeach coded video sequence is independent from other coded videosequences. Each video sequence may be associated with multiple videoframes or images. The coded video sequence may be received from achannel (501), which may be a hardware/software link to a storage devicewhich stores the encoded video data or a streaming source whichtransmits the encoded video data. The receiver (531) may receive theencoded video data with other data such as coded audio data and/orancillary data streams, that may be forwarded to their respectiveprocessing circuitry (not depicted). The receiver (531) may separate thecoded video sequence from the other data. To combat network jitter, abuffer memory (515) may be disposed in between the receiver (531) and anentropy decoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) may be implemented as part of thevideo decoder (510). In other applications, it can be outside of andseparate from the video decoder (510) (not depicted). In still otherapplications, there can be a buffer memory (not depicted) outside of thevideo decoder (510) for the purpose of, for example, combating networkjitter, and there may be another additional buffer memory (515) insidethe video decoder (510), for example to handle playback timing. When thereceiver (531) is receiving data from a store/forward device ofsufficient bandwidth and controllability, or from an isosynchronousnetwork, the buffer memory (515) may not be needed, or can be small. Foruse on best-effort packet networks such as the Internet, the buffermemory (515) of sufficient size may be required, and its size can becomparatively large. Such buffer memory may be implemented with anadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such asdisplay (512) (e.g., a display screen) that may or may not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as is shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received by theparser (520). The entropy coding of the coded video sequence can be inaccordance with a video coding technology or standard, and can followvarious principles, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (520) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thesubgroups. The subgroups can include Groups of Pictures (GOPs),pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks,Transform Units (TUs), Prediction Units (PUs) and so forth. The parser(520) may also extract from the coded video sequence information such astransform coefficients (e.g., Fourier transform coefficients), quantizerparameter values, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple differentprocessing or functional units depending on the type of the coded videopicture or parts thereof (such as: inter and intra picture, inter andintra block), and other factors. The units that are involved and howthey are involved may be controlled by the subgroup control informationthat was parsed from the coded video sequence by the parser (520). Theflow of such subgroup control information between the parser (520) andthe multiple processing or functional units below is not depicted forsimplicity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these functional units interact closelywith each other and can, at least partly, be integrated with oneanother. However, for the purpose of describing the various functions ofthe disclosed subject matter with clarity, the conceptual subdivisioninto the functional units is adopted in the disclosure below.

A first unit may include the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) may receive a quantized transformcoefficient as well as control information, including informationindicating which type of inverse transform to use, block size,quantization factor/parameters, quantization scaling matrices, and thelie as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values that canbe input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block, i.e., a block that does not usepredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) may generate a block of the same size and shape ofthe block under reconstruction using surrounding block information thatis already reconstructed and stored in the current picture buffer (558).The current picture buffer (558) buffers, for example, partlyreconstructed current picture and/or fully reconstructed currentpicture. The aggregator (555), in some implementations, may add, on aper sample basis, the prediction information the intra prediction unit(552) has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forinter-picture prediction. After motion compensating the fetched samplesin accordance with the symbols (521) pertaining to the block, thesesamples can be added by the aggregator (555) to the output of thescaler/inverse transform unit (551) (output of unit 551 may be referredto as the residual samples or residual signal) so as to generate outputsample information. The addresses within the reference picture memory(557) from where the motion compensation prediction unit (553) fetchesprediction samples can be controlled by motion vectors, available to themotion compensation prediction unit (553) in the form of symbols (521)that can have, for example X, Y components (shift), and referencepicture components (time). Motion compensation may also includeinterpolation of sample values as fetched from the reference picturememory (557) when sub-sample exact motion vectors are in use, and mayalso be associated with motion vector prediction mechanisms, and soforth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values. Several type of loop filters may beincluded as part of the loop filter unit 556 in various orders, as willbe described in further detail below.

The output of the loop filter unit (556) can be a sample stream that canbe output to the rendering device (512) as well as stored in thereference picture memory (557) for use in future inter-pictureprediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future inter-picture prediction. For example,once a coded picture corresponding to a current picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, the parser (520)), the current picture buffer(558) can become a part of the reference picture memory (557), and afresh current picture buffer can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology adopted in a standard, suchas ITU-T Rec. H.265. The coded video sequence may conform to a syntaxspecified by the video compression technology or standard being used, inthe sense that the coded video sequence adheres to both the syntax ofthe video compression technology or standard and the profiles asdocumented in the video compression technology or standard.Specifically, a profile can select certain tools from all the toolsavailable in the video compression technology or standard as the onlytools available for use under that profile. To be standard-compliant,the complexity of the coded video sequence may be within bounds asdefined by the level of the video compression technology or standard. Insome cases, levels restrict the maximum picture size, maximum framerate, maximum reconstruction sample rate (measured in, for examplemegasamples per second), maximum reference picture size, and so on.Limits set by levels can, in some cases, be further restricted throughHypothetical Reference Decoder (HRD) specifications and metadata for HRDbuffer management signaled in the coded video sequence.

In some example embodiments, the receiver (531) may receive additional(redundant) data with the encoded video. The additional data may beincluded as part of the coded video sequence(s). The additional data maybe used by the video decoder (510) to properly decode the data and/or tomore accurately reconstruct the original video data. Additional data canbe in the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anexample embodiment of the present disclosure. The video encoder (603)may be included in an electronic device (620). The electronic device(620) may further include a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in place of the videoencoder (403) in the example of FIG. 4 .

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the example ofFIG. 6 ) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) may beimplemented as a portion of the electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 YCrCb, RGB, XYZ . . .), and any suitable sampling structure (for example YCrCb 4:2:0, YCrCb4:4:4). In a media serving system, the video source (601) may be astorage device capable of storing previously prepared video. In avideoconferencing system, the video source (601) may be a camera thatcaptures local image information as a video sequence. Video data may beprovided as a plurality of individual pictures or images that impartmotion when viewed in sequence. The pictures themselves may be organizedas a spatial array of pixels, wherein each pixel can comprise one ormore samples depending on the sampling structure, color space, and thelike being in use. A person having ordinary skill in the art can readilyunderstand the relationship between pixels and samples. The descriptionbelow focuses on samples.

According to some example embodiments, the video encoder (603) may codeand compress the pictures of the source video sequence into a codedvideo sequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speedconstitutes one function of a controller (650). In some embodiments, thecontroller (650) may be functionally coupled to and control otherfunctional units as described below. The coupling is not depicted forsimplicity. Parameters set by the controller (650) can include ratecontrol related parameters (picture skip, quantizer, lambda value ofrate-distortion optimization techniques, . . . ), picture size, group ofpictures (GOP) layout, maximum motion vector search range, and the like.The controller (650) can be configured to have other suitable functionsthat pertain to the video encoder (603) optimized for a certain systemdesign.

In some example embodiments, the video encoder (603) may be configuredto operate in a coding loop. As an oversimplified description, in anexample, the coding loop can include a source coder (630) (e.g.,responsible for creating symbols, such as a symbol stream, based on aninput picture to be coded, and a reference picture(s)), and a (local)decoder (633) embedded in the video encoder (603). The decoder (633)reconstructs the symbols to create the sample data in a similar manneras a (remote) decoder would create even though the embedded decoder 633process coded video steam by the source coder 630 without entropy coding(as any compression between symbols and coded video bitstream in entropycoding may be lossless in the video compression technologies consideredin the disclosed subject matter). The reconstructed sample stream(sample data) is input to the reference picture memory (634). As thedecoding of a symbol stream leads to bit-exact results independent ofdecoder location (local or remote), the content in the reference picturememory (634) is also bit exact between the local encoder and remoteencoder. In other words, the prediction part of an encoder “sees” asreference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used to improve coding quality.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633) inthe encoder.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that may only be presentin a decoder also may necessarily need to be present, in substantiallyidentical functional form, in a corresponding encoder. For this reason,the disclosed subject matter may at times focus on decoder operation,which allies to the decoding portion of the encoder. The description ofencoder technologies can thus be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas or aspects a more detail description of the encoder is providedbelow.

During operation in some example implementations, the source coder (630)may perform motion compensated predictive coding, which codes an inputpicture predictively with reference to one or more previously codedpicture from the video sequence that were designated as “referencepictures.” In this manner, the coding engine (632) codes differences (orresidue) in the color channels between pixel blocks of an input pictureand pixel blocks of reference picture(s) that may be selected asprediction reference(s) to the input picture. The term “residue” and itsadjective form “residual” may be used interchangeably.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end (remote) video decoder (absent transmissionerrors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compression of the symbols accordingto technologies such as Huffman coding, variable length coding,arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person having ordinary skill in the art is aware of thosevariants of I pictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample coding blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16samples each) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures. The sourcepictures or the intermediate processed pictures may be subdivided intoother types of blocks for other purposes. The division of coding blocksand the other types of blocks may or may not follow the same manner, asdescribed in further detail below.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data may accordingly conform to a syntax specified bythe video coding technology or standard being used.

In some example embodiments, the transmitter (640) may transmitadditional data with the encoded video. The source coder (630) mayinclude such data as part of the coded video sequence. The additionaldata may comprise temporal/spatial/SNR enhancement layers, other formsof redundant data such as redundant pictures and slices, SEI messages,VUI parameter set fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) utilizes spatial correlation in a givenpicture, and inter-picture prediction utilizes temporal or othercorrelation between the pictures. For example, a specific picture underencoding/decoding, which is referred to as a current picture, may bepartitioned into blocks. A block in the current picture, when similar toa reference block in a previously coded and still buffered referencepicture in the video, may be coded by a vector that is referred to as amotion vector. The motion vector points to the reference block in thereference picture, and can have a third dimension identifying thereference picture, in case multiple reference pictures are in use.

In some example embodiments, a bi-prediction technique can be used forinter-picture prediction. According to such bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that both proceed the current picture in the video indecoding order (but may be in the past or future, respectively, indisplay order) are used. A block in the current picture can be coded bya first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bejointly predicted by a combination of the first reference block and thesecond reference block.

Further, a merge mode technique may be used in the inter-pictureprediction to improve coding efficiency.

According to some example embodiments of the disclosure, predictions,such as inter-picture predictions and intra-picture predictions areperformed in the unit of blocks. For example, a picture in a sequence ofvideo pictures is partitioned into coding tree units (CTU) forcompression, the CTUs in a picture may have the same size, such as 64×64pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may includethree parallel coding tree blocks (CTBs): one luma CTB and two chromaCTBs. Each CTU can be recursively quadtree split into one or multiplecoding units (CUs). For example, a CTU of 64×64 pixels can be split intoone CU of 64×64 pixels, or 4 CUs of 32×32 pixels. Each of the one ormore of the 32×32 block may be further split into 4 CUs of 16×16 pixels.In some example embodiments, each CU may be analyzed during encoding todetermine a prediction type for the CU among various prediction typessuch as an inter prediction type or an intra prediction type. The CU maybe split into one or more prediction units (PUs) depending on thetemporal and/or spatial predictability. Generally, each PU includes aluma prediction block (PB), and two chroma PBs. In an embodiment, aprediction operation in coding (encoding/decoding) is performed in theunit of a prediction block. The split of a CU into PU (or PBs ofdifferent color channels) may be performed in various spatial pattern. Aluma or chroma PB, for example, may include a matrix of values (e.g.,luma values) for samples, such as 8×8 pixels, 16×16 pixels, 8×16 pixels,16×8 samples, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherexample embodiment of the disclosure. The video encoder (703) isconfigured to receive a processing block (e.g., a prediction block) ofsample values within a current video picture in a sequence of videopictures, and encode the processing block into a coded picture that ispart of a coded video sequence. The example video encoder (703) may beused in place of the video encoder (403) in the FIG. 4 example.

For example, the video encoder (703) receives a matrix of sample valuesfor a processing block, such as a prediction block of 8×8 samples, andthe like. The video encoder (703) then determines whether the processingblock is best coded using intra mode, inter mode, or bi-prediction modeusing, for example, rate-distortion optimization (RDO). When theprocessing block is determined to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis determined to be coded in inter mode or bi-prediction mode, the videoencoder (703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Insome example embodiments, a merge mode may be used as a submode of theinter picture prediction where the motion vector is derived from one ormore motion vector predictors without the benefit of a coded motionvector component outside the predictors. In some other exampleembodiments, a motion vector component applicable to the subject blockmay be present. Accordingly, the video encoder (703) may includecomponents not explicitly shown in FIG. 7 , such as a mode decisionmodule, to determine the perdition mode of the processing blocks.

In the example of FIG. 7 , the video encoder (703) includes an interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in the examplearrangement in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures in display order), generate inter predictioninformation (e.g., description of redundant information according tointer encoding technique, motion vectors, merge mode information), andcalculate inter prediction results (e.g., predicted block) based on theinter prediction information using any suitable technique. In someexamples, the reference pictures are decoded reference pictures that aredecoded based on the encoded video information using the decoding unit633 embedded in the example encoder 620 of FIG. 6 (shown as residualdecoder 728 of FIG. 7 , as described in further detail below).

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to blocksalready coded in the same picture, and generate quantized coefficientsafter transform, and in some cases also to generate intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). The intra encoder (722) maycalculates intra prediction results (e.g., predicted block) based on theintra prediction information and reference blocks in the same picture.

The general controller (721) may be configured to determine generalcontrol data and control other components of the video encoder (703)based on the general control data. In an example, the general controller(721) determines the prediction mode of the block, and provides acontrol signal to the switch (726) based on the prediction mode. Forexample, when the prediction mode is the intra mode, the generalcontroller (721) controls the switch (726) to select the intra moderesult for use by the residue calculator (723), and controls the entropyencoder (725) to select the intra prediction information and include theintra prediction information in the bitstream; and when the predicationmode for the block is the inter mode, the general controller (721)controls the switch (726) to select the inter prediction result for useby the residue calculator (723), and controls the entropy encoder (725)to select the inter prediction information and include the interprediction information in the bitstream.

The residue calculator (723) may be configured to calculate a difference(residue data) between the received block and prediction results for theblock selected from the intra encoder (722) or the inter encoder (730).The residue encoder (724) may be configured to encode the residue datato generate transform coefficients. For example, the residue encoder(724) may be configured to convert the residue data from a spatialdomain to a frequency domain to generate the transform coefficients. Thetransform coefficients are then subject to quantization processing toobtain quantized transform coefficients. In various example embodiments,the video encoder (703) also includes a residual decoder (728). Theresidual decoder (728) is configured to perform inverse-transform, andgenerate the decoded residue data. The decoded residue data can besuitably used by the intra encoder (722) and the inter encoder (730).For example, the inter encoder (730) can generate decoded blocks basedon the decoded residue data and inter prediction information, and theintra encoder (722) can generate decoded blocks based on the decodedresidue data and the intra prediction information. The decoded blocksare suitably processed to generate decoded pictures and the decodedpictures can be buffered in a memory circuit (not shown) and used asreference pictures.

The entropy encoder (725) may be configured to format the bitstream toinclude the encoded block and perform entropy coding. The entropyencoder (725) is configured to include in the bitstream variousinformation. For example, the entropy encoder (725) may be configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. When coding a block in the merge submode of either inter modeor bi-prediction mode, there may be no residue information.

FIG. 8 shows a diagram of an example video decoder (810) according toanother embodiment of the disclosure. The video decoder (810) isconfigured to receive coded pictures that are part of a coded videosequence, and decode the coded pictures to generate reconstructedpictures. In an example, the video decoder (810) may be used in place ofthe video decoder (410) in the example of FIG. 4 .

In the example of FIG. 8 , the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residual decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in the example arrangement of FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (e.g., intra mode, intermode, bi-predicted mode, merge submode or another submode), predictioninformation (e.g., intra prediction information or inter predictioninformation) that can identify certain sample or metadata used forprediction by the intra decoder (872) or the inter decoder (880),residual information in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isthe inter or bi-predicted mode, the inter prediction information isprovided to the inter decoder (880); and when the prediction type is theintra prediction type, the intra prediction information is provided tothe intra decoder (872). The residual information can be subject toinverse quantization and is provided to the residual decoder (873).

The inter decoder (880) may be configured to receive the interprediction information, and generate inter prediction results based onthe inter prediction information.

The intra decoder (872) may be configured to receive the intraprediction information, and generate prediction results based on theintra prediction information.

The residual decoder (873) may be configured to perform inversequantization to extract de-quantized transform coefficients, and processthe de-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residual decoder (873) mayalso utilize certain control information (to include the QuantizerParameter (QP)) which may be provided by the entropy decoder (871) (datapath not depicted as this may be low data volume control informationonly).

The reconstruction module (874) may be configured to combine, in thespatial domain, the residual as output by the residual decoder (873) andthe prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block forming partof the reconstructed picture as part of the reconstructed video. It isnoted that other suitable operations, such as a deblocking operation andthe like, may also be performed to improve the visual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In some example embodiments, the video encoders(403), (603), and (703), and the video decoders (410), (510), and (810)can be implemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Turning to block partitioning for coding and decoding, generalpartitioning may start from a base block and may follow a predefinedruleset, particular patterns, partition trees, or any partitionstructure or scheme. The partitioning may be hierarchical and recursive.After dividing or partitioning a base block following any of the examplepartitioning procedures or other procedures described below, or thecombination thereof, a final set of partitions or coding blocks may beobtained. Each of these partitions may be at one of various partitioninglevels in the partitioning hierarchy, and may be of various shapes. Eachof the partitions may be referred to as a coding block (CB). For thevarious example partitioning implementations described further below,each resulting CB may be of any of the allowed sizes and partitioninglevels. Such partitions are referred to as coding blocks because theymay form units for which some basic coding/decoding decisions may bemade and coding/decoding parameters may be optimized, determined, andsignaled in an encoded video bitstream. The highest or deepest level inthe final partitions represents the depth of the coding blockpartitioning structure of tree. A coding block may be a luma codingblock or a chroma coding block. The CB tree structure of each color maybe referred to as coding block tree (CBT).

The coding blocks of all color channels may collectively be referred toas a coding unit (CU). The hierarchical structure of for all colorchannels may be collectively referred to as coding tree unit (CTU). Thepartitioning patterns or structures for the various color channels in ina CTU may or may not be the same.

In some implementations, partition tree schemes or structures used forthe luma and chroma channels may not need to be the same. In otherwords, luma and chroma channels may have separate coding tree structuresor patterns. Further, whether the luma and chroma channels use the sameor different coding partition tree structures and the actual codingpartition tree structures to be used may depend on whether the slicebeing coded is a P, B, or I slice. For example, For an I slice, thechroma channels and luma channel may have separate coding partition treestructures or coding partition tree structure modes, whereas for a P orB slice, the luma and chroma channels may share a same coding partitiontree scheme. When separate coding partition tree structures or modes areapplied, a luma channel may be partitioned into CBs by one codingpartition tree structure, and a chroma channel may be partitioned intochroma CBs by another coding partition tree structure.

In some example implementations, a predetermined partitioning patternmay be applied to a base block. As shown in FIG. 9 , an example 4-waypartition tree may start from a first predefined level (e.g., 64×64block level or other sizes, as a base block size) and a base block maybe partitioned hierarchically down to a predefined lowest level (e.g.,4×4 level). For example, a base block may be subject to four predefinedpartitioning options or patterns indicated by 902, 904, 906, and 908,with the partitions designated as R being allowed for recursivepartitioning in that the same partition options as indicated in FIG. 9may be repeated at a lower scale until the lowest level (e.g., 4×4level). In some implementations, additional restrictions may be appliedto the partitioning scheme of FIG. 9 . In the implementation of FIG. 9 ,rectangular partitions (e.g., 1:2/2:1 rectangular partitions) may beallowed but they may not be allowed to be recursive, whereas squarepartitions are allowed to be recursive. The partitioning following FIG.9 with recursion, if needed, generates a final set of coding blocks. Acoding tree depth may be further defined to indicate the splitting depthfrom the root node or root block. For example, the coding tree depth forthe root node or root block, e.g. a 64×64 block, may be set to 0, andafter the root block is further split once following FIG. 9 , the codingtree depth is increased by 1. The maximum or deepest level from 64×64base block to a minimum partition of 4×4 would be 4 (starting from level0) for the scheme above. Such partitioning scheme may apply to one ormore of the color channels. Each color channel may be partitionedindependently following the scheme of FIG. 9 (e.g., partitioning patternor option among the predefined patterns may be independently determinedfor each of the color channels at each hierarchical level).Alternatively, two or more of the color channels may share the samehierarchical pattern tree of FIG. 9 (e.g., the same partitioning patternor option among the predefined patterns may be chosen for the two ormore color channels at each hierarchical level).

FIG. 10 shows another example predefined partitioning pattern allowingrecursive partitioning to form a partitioning tree. As shown in FIG. 10, an example 10-way partitioning structure or pattern may be predefined.The root block may start at a predefined level (e.g. from a base blockat 128×128 level, or 64×64 level). The example partitioning structure ofFIG. 10 includes various 2:1/1:2 and 4:1/1:4 rectangular partitions. Thepartition types with 3 sub-partitions indicated 1002, 1004, 1006, and1008 in the second row of FIG. 10 may be referred to “T-type”partitions. The “T-Type” partitions 1002, 1004, 1006, and 1008 may bereferred to as Left T-Type, Top T-Type, Right T-Type and Bottom T-Type.In some example implementations, none of the rectangular partitions ofFIG. 10 is allowed to be further subdivided. A coding tree depth may befurther defined to indicate the splitting depth from the root node orroot block. For example, the coding tree depth for the root node or rootblock, e.g., a 128×128 block, may be set to 0, and after the root blockis further split once following FIG. 10 , the coding tree depth isincreased by 1. In some implementations, only the all-square partitionsin 1010 may be allowed for recursive partitioning into the next level ofthe partitioning tree following pattern of FIG. 10 . In other words,recursive partitioning may not be allowed for the square partitionswithin the T-type patterns 1002, 1004, 1006, and 1008. The partitioningprocedure following FIG. 10 with recursion, if needed, generates a finalset of coding blocks. Such scheme may apply to one or more of the colorchannels. In some implementations, more flexibility may be added to theuse of partitions below 8×8 level. For example, 2×2 chroma interprediction may be used in certain cases.

In some other example implementations for coding block partitioning, aquadtree structure may be used for splitting a base block or anintermediate block into quadtree partitions. Such quadtree splitting maybe applied hierarchically and recursively to any square shapedpartitions. Whether a base block or an intermediate block or partitionis further quadtree split may be adapted to various localcharacteristics of the base block or intermediate block/partition.Quadtree partitioning at picture boundaries may be further adapted. Forexample, implicit quadtree split may be performed at picture boundary sothat a block will keep quadtree splitting until the size fits thepicture boundary.

In some other example implementations, a hierarchical binarypartitioning from a base block may be used. For such a scheme, the baseblock or an intermediate level block may be partitioned into twopartitions. A binary partitioning may be either horizontal or vertical.For example, a horizontal binary partitioning may split a base block orintermediate block into equal right and left partitions. Likewise, avertical binary partitioning may split a base block or intermediateblock into equal upper and lower partitions. Such binary partitioningmay be hierarchical and recursive. Decision may be made at each of thebase block or intermediate block whether the binary partitioning schemeshould continue, and if the scheme does continue further, whether ahorizontal or vertical binary partitioning should be used. In someimplementations, further partitioning may stop at a predefined lowestpartition size (in either one or both dimensions). Alternatively,further partitioning may stop once a predefined partitioning level ordepth from the base block is reached. In some implementations, theaspect ratio of a partition may be restricted. For example, the aspectratio of a partition may not be smaller than 1:4 (or larger than 4:1).As such, a vertical strip partition with vertical to horizontal aspectratio of 4:1, may only be further binary partitioned vertically into anupper and lower partitions each having a vertical to horizontal aspectratio of 2:1.

In yet some other examples, a ternary partitioning scheme may be usedfor partitioning a base block or any intermediate block, as shown inFIG. 13 . The ternary pattern may be implemented vertical, as shown in1302 of FIG. 13 , or horizontal, as shown in 1304 of FIG. 13 . While theexample split ratio in FIG. 13 , either vertically or horizontally, isshown as 1:2:1, other ratios may be predefined. In some implementations,two or more different ratios may be predefined. Such ternarypartitioning scheme may be used to complement the quadtree or binarypartitioning structures in that such triple-tree partitioning is capableof capturing objects located in block center in one contiguous partitionwhile quadtree and binary-tree are always splitting along block centerand thus would split the object into separate partitions. In someimplementations, the width and height of the partitions of the exampletriple trees are always power of 2 to avoid additional transforms.

The above partitioning schemes may be combined in any manner atdifferent partitioning levels. As one example, the quadtree and thebinary partitioning schemes described above may be combined to partitiona base block into a quadtree-binary-tree (QTBT) structure. In such ascheme, a base block or an intermediate block/partition may be eitherquadtree split or binary split, subject to a set of predefinedconditions, if specified. A particular example is illustrated in FIG. 14. In the example of FIG. 14 , a base block is first quadtree split intofour partitions, as shown by 1402, 1404, 1406, and 1408. Thereafter,each of the resulting partitions is either quadtree partitioned intofour further partitions (such as 1408), or binarily split into twofurther partitions (either horizontally or vertically, such as 1402 or1406, both being symmetric, for example) at the next level, or non-split(such as 1404). Binary or quadtree splitting may be allowed recursivelyfor square shaped partitions, as shown by the overall example partitionpattern of 1410 and the corresponding tree structure/representation in1420, in which the solid lines represent quadtree splitting, and thedashed lines represent binary splitting. Flags may be used for eachbinary splitting node (non-leaf binary partitions) to indicate whetherthe binary splitting is horizontal or vertical. For example, as shown in1420, consistent with the partitioning structure of 1410, flag “0” mayrepresent horizontal binary splitting, and flag “1” may representvertical binary splitting. For the quadtree-split partition, there is noneed to indicate the splitting type since quadtree splitting alwayssplits a block or a partition both horizontally and vertically toproduce 4 sub-blocks/partitions with an equal size. In someimplementations, flag “1” may represent horizontal binary splitting, andflag “0” may represent vertical binary splitting.

In some example implementations of the QTBT, the quadtree and binarysplitting ruleset may be represented by the following predefinedparameters and the corresponding functions associated therewith:

-   -   CTU size: the root node size of a quadtree (size of a base        block)    -   MinQTSize: the minimum allowed quadtree leaf node size    -   MaxBTSize: the maximum allowed binary tree root node size    -   MaxBTDepth: the maximum allowed binary tree depth    -   MinBTSize: the minimum allowed binary tree leaf node size        In some example implementations of the QTBT partitioning        structure, the CTU size may be set as 128×128 luma samples with        two corresponding 64×64 blocks of chroma samples (when an        example chroma sub-sampling is considered and used), the        MinQTSize may be set as 16×16, the MaxBTSize may be set as        64×64, the MinBTSize (for both width and height) may be set as        4×4, and the MaxBTDepth may be set as 4. The quadtree        partitioning may be applied to the CTU first to generate        quadtree leaf nodes. The quadtree leaf nodes may have a size        from its minimum allowed size of 16×16 (i.e., the MinQTSize) to        128×128 (i.e., the CTU size). If a node is 128×128, it will not        be first split by the binary tree since the size exceeds the        MaxBTSize (i.e., 64×64). Otherwise, nodes which do not exceed        MaxBTSize could be partitioned by the binary tree. In the        example of FIG. 14 , the base block is 128×128. The basic block        can only be quadtree split, according to the predefined ruleset.        The base block has a partitioning depth of 0. Each of the        resulting four partitions are 64×64, not exceeding MaxBTSize,        may be further quadtree or binary-tree split at level 1. The        process continues. When the binary tree depth reaches MaxBTDepth        (i.e., 4), no further splitting may be considered. When the        binary tree node has width equal to MinBTSize (i.e., 4), no        further horizontal splitting may be considered. Similarly, when        the binary tree node has height equal to MinBTSize, no further        vertical splitting is considered.

In some example implementations, the QTBT scheme above may be configuredto support a flexibility for the luma and chroma to have the same QTBTstructure or separate QTBT structures. For example, for P and B slices,the luma and chroma CTBs in one CTU may share the same QTBT structure.However, for I slices, the luma CTBs maybe partitioned into CBs by aQTBT structure, and the chroma CTBs may be partitioned into chroma CBsby another QTBT structure. This means that a CU may be used to refer todifferent color channels in an I slice, e.g., the I slice may consist ofa coding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice may consist of coding blocks ofall three colour components.

In some other implementations, the QTBT scheme may be supplemented withternary scheme described above. Such implementations may be referred toas multi-type-tree (MTT) structure. For example, in addition to binarysplitting of a node, one of the ternary partition patterns of FIG. 13may be chosen. In some implementations, only square nodes may be subjectto ternary splitting. An additional flag may be used to indicate whethera ternary partitioning is horizontal or vertical.

The design of two-level or multi-level tree such as the QTBTimplementations and QTBT implementations supplemented by ternarysplitting may be mainly motivated by complexity reduction.Theoretically, the complexity of traversing a tree is T^(D), where Tdenotes the number of split types, and D is the depth of tree. Atradeoff may be made by using multiple types (T) while reducing thedepth (D).

In some implementations, a CB may be further partitioned. For example, aCB may be further partitioned into multiple prediction blocks (PBs) forpurposes of intra or inter-frame prediction during coding and decodingprocesses. In other words, a CB may be further divided into differentsubpartitions, where individual prediction decision/configuration may bemade. In parallel, a CB may be further partitioned into a plurality oftransform blocks (TBs) for purposes of delineating levels at whichtransform or inverse transform of video data is performed. Thepartitioning scheme of a CB into PBs and TBs may or may not be the same.For example, each partitioning scheme may be performed using its ownprocedure based on, for example, the various characteristics of thevideo data. The PB and TB partitioning schemes may be independent insome example implementations. The PB and TB partitioning schemes andboundaries may be correlated in some other example implementations. Isome implementations, for example, TBs may be partitioned after PBpartitions, and in particular, each PB, after being determined followingpartitioning of a coding block, may then be further partitioned into oneor more TBs. For example, in some implementations, a PB may be splitinto one, two, four, or other number of TBs.

In some implementations, for partitioning of a base block into codingblocks and further into prediction blocks and/or transform blocks, theluma channel and the chroma channels may be treated differently. Forexample, in some implementations, partitioning of a coding block intoprediction blocks and/or transform blocks may be allowed for the lumachannel, whereas such partitioning of a coding block into predictionblocks and/or transform blocks may not be allowed for the chromachannel(s). In such implementations, transform and/or prediction of lumablocks thus may be performed only at the coding block level. For anotherexample, minimum transform block size for luma channel and chromachannel(s) may be different, e.g., coding blocks for luma channel may beallowed to be partitioned into smaller transform and/or predictionblocks than the chroma channels. For yet another example, the maximumdepth of partitioning of a coding block into transform blocks and/orprediction blocks may be different between the luma channel and thechroma channels, e.g., coding blocks for luma channel may be allowed tobe partitioned into deeper transform and/or prediction blocks than thechroma channel(s). For a specific example, luma coding blocks may bepartitioned into transform blocks of multiple sizes that can berepresented by a recursive partition going down by up to 2 levels, andtransform block shapes such as square, 2:1/1:2, and 4:1/1:4 andtransform block size from 4×4 to 64×64 may be allowed. For chromablocks, however, only the largest possible transform blocks specifiedfor the luma blocks may be allowed.

In some example implementations for partitioning of a coding block intoPBs, the depth, the shape, and/or other characteristics of the PBpartitioning may depend on whether the PB is intra or inter coded.

The partitioning of a coding block (or a prediction block) intotransform blocks may be implemented in various example schemes,including but not limited to quadtree splitting and predefined patternsplitting, recursively or non-recursively, and with additionalconsideration for transform blocks at the boundary of the coding blockor prediction block. In general, the resulting transform blocks may beat different split levels, may not be of the same size, and may not needto be square in shape (e.g., they can be rectangular with some allowedsizes and aspect ratios). Further examples are descried in furtherdetail below in relation to FIGS. 15, 16 and 17 .

In some other implementations, however, the CBs obtained via any of thepartitioning schemes above may be used as a basic or smallest codingblock for prediction and/or transform. In other words, no furthersplitting is performed for perform inter-prediction/intra-predictionpurposes and/or for transform purposes. For example, CBs obtained fromthe QTBT scheme above may be directly used as the units for performingpredictions. Specifically, such a QTBT structure removes the concepts ofmultiple partition types, i.e. it removes the separation of the CU, PUand TU, and supports more flexibility for CU/CB partition shapes asdescribed above. In such QTBT block structure, a CU/CB can have either asquare or rectangular shape. The leaf nodes of such QTBT are used asunits for prediction and transform processing without any furtherpartitioning. This means that the CU, PU and TU have the same block sizein such example QTBT coding block structure.

The various CB partitioning schemes above and the further partitioningof CBs into PBs and/or TBs (including no PB/TB partitioning) may becombined in any manner. The following particular implementations areprovided as non-limiting examples.

A specific example implementation of coding block and transform blockpartitioning is described below. In such an example implementation, abase block may be split into coding blocks using recursive quadtreesplitting, or a predefined splitting pattern described above (such asthose in FIG. 9 and FIG. 10 ). At each level, whether further quadtreesplitting of a particular partition should continue may be determined bylocal video data characteristics. The resulting CBs may be at variousquadtree splitting levels, and of various sizes. The decision on whetherto code a picture area using inter-picture (temporal) or intra-picture(spatial) prediction may be made at the CB level (or CU level, for allthree-color channels). Each CB may be further split into one, two, four,or other number of PBs according to predefined PB splitting type. Insideone PB, the same prediction process may be applied and the relevantinformation may be transmitted to the decoder on a PB basis. Afterobtaining the residual block by applying the prediction process based onthe PB splitting type, a CB can be partitioned into TBs according toanother quadtree structure similar to the coding tree for the CB. Inthis particular implementation, a CB or a TB may but does not have to belimited to square shape. Further in this particular example, a PB may besquare or rectangular shape for an inter-prediction and may only besquare for intra-prediction. A coding block may be split into, e.g.,four square-shaped TBs. Each TB may be further split recursively (usingquadtree split) into smaller TBs, referred to as Residual Quadtree(RQT).

Another example implementation for partitioning of a base block intoCBs, PBs and or TBs is further described below. For example, rather thanusing a multiple partition unit types such as those shown in FIG. 9 orFIG. 10 , a quadtree with nested multi-type tree using binary andternary splits segmentation structure (e.g., the QTBT or QTBT withternary splitting as descried above) may be used. The separation of theCB, PB and TB (i.e., the partitioning of CB into PBs and/or TBs, and thepartitioning of PBs into TBs) may be abandoned except when needed forCBs that have a size too large for the maximum transform length, wheresuch CBs may need further splitting. This example partitioning schememay be designed to support more flexibility for CB partition shapes sothat the prediction and transform can both be performed on the CB levelwithout further partitioning. In such a coding tree structure, a CB mayhave either a square or rectangular shape. Specifically, a coding treeblock (CTB) may be first partitioned by a quadtree structure. Then thequadtree leaf nodes may be further partitioned by a nested multi-typetree structure. An example of the nested multi-type tree structure usingbinary or ternary splitting is shown in FIG. 11 . Specifically, theexample multi-type tree structure of FIG. 11 includes four splittingtypes, referred to as vertical binary splitting (SPLIT_BT_VER) (1102),horizontal binary splitting (SPLIT_BT_HOR) (1104), vertical ternarysplitting (SPLIT_TT_VER) (1106), and horizontal ternary splitting(SPLIT_TT_HOR) (1108). The CBs then correspond to leaves of themulti-type tree. In this example implementation, unless the CB is toolarge for the maximum transform length, this segmentation is used forboth prediction and transform processing without any furtherpartitioning. This means that, in most cases, the CB, PB and TB have thesame block size in the quadtree with nested multi-type tree coding blockstructure. The exception occurs when maximum supported transform lengthis smaller than the width or height of the colour component of the CB.In some implementations, in addition to the binary or ternary splitting,the nested patterns of FIG. 11 may further include quadtree splitting.

One specific example for the quadtree with nested multi-type tree codingblock structure of block partition (including quadtree, binary, andternary splitting options) for one base block is shown in FIG. 12 . Inmore detail, FIG. 12 shows that the base block 1200 is quadtree splitinto four square partitions 1202, 1204, 1206, and 1208. Decision tofurther use the multi-type tree structure of FIG. 11 and quadtree forfurther splitting is made for each of the quadtree-split partitions. Inthe example of FIG. 12 , partition 1204 is not further split. Partitions1202 and 1208 each adopt another quadtree split. For partition 1202, thesecond level quadtree-split top-left, top-right, bottom-left, andbottom-right partitions adopts third level splitting of quadtree,horizontal binary splitting 1104 of FIG. 11 , non-splitting, andhorizontal ternary splitting 1108 of FIG. 11 , respectively. Partition1208 adopts another quadtree split, and the second level quadtree-splittop-left, top-right, bottom-left, and bottom-right partitions adoptsthird level splitting of vertical ternary splitting 1106 of FIG. 11 ,non-splitting, non-splitting, and horizontal binary splitting 1104 ofFIG. 11 , respectively. Two of the subpartitions of the third-leveltop-left partition of 1208 are further split according to horizontalbinary splitting 1104 and horizontal ternary splitting 1108 of FIG. 11 ,respectively. Partition 1206 adopts a second level split patternfollowing the vertical binary splitting 1102 of FIG. 11 into twopartitions which are further split in a third-level according tohorizontal ternary splitting 1108 and vertical binary splitting 1102 ofthe FIG. 11 . A fourth level splitting is further applied to one of themaccording to horizontal binary splitting 1104 of FIG. 11 .

For the specific example above, the maximum luma transform size may be64×64 and the maximum supported chroma transform size could be differentfrom the luma at, e.g., 32×32. Even though the example CBs above in FIG.12 are generally not further split into smaller PBs and/or TBs, when thewidth or height of the luma coding block or chroma coding block islarger than the maximum transform width or height, the luma coding blockor chroma coding block may be automatically split in the horizontaland/or vertical direction to meet the transform size restriction in thatdirection.

In the specific example for partitioning of a base block into CBs above,and as descried above, the coding tree scheme may support the abilityfor the luma and chroma to have a separate block tree structure. Forexample, for P and B slices, the luma and chroma CTBs in one CTU mayshare the same coding tree structure. For I slices, for example, theluma and chroma may have separate coding block tree structures. Whenseparate block tree structures are applied, luma CTB may be partitionedinto luma CBs by one coding tree structure, and the chroma CTBs arepartitioned into chroma CBs by another coding tree structure. This meansthat a CU in an I slice may consist of a coding block of the lumacomponent or coding blocks of two chroma components, and a CU in a P orB slice always consists of coding blocks of all three colour componentsunless the video is monochrome.

When a coding block is further partitioned into multiple transformblocks, the transform blocks therein may be order in the bitstreamfollowing various order or scanning manners. Example implementations forpartitioning a coding block or prediction block into transform blocks,and a coding order of the transform blocks are described in furtherdetail below. In some example implementations, as descried above, atransform partitioning may support transform blocks of multiple shapes,e.g., 1:1 (square), 1:2/2:1, and 1:4/4:1, with transform block sizesranging from, e.g., 4×4 to 64×64. In some implementations, if the codingblock is smaller than or equal to 64×64, the transform blockpartitioning may only apply to luma component, such that for chromablocks, the transform block size is identical to the coding block size.Otherwise, if the coding block width or height is greater than 64, thenboth the luma and chroma coding blocks may be implicitly split intomultiples of min (W, 64)×min (H, 64) and min (W, 32)×min (H, 32)transform blocks, respectively.

In some example implementations of transform block partitioning, forboth intra and inter coded blocks, a coding block may be furtherpartitioned into multiple transform blocks with a partitioning depth upto a predefined number of levels (e.g., 2 levels). The transform blockpartitioning depth and sizes may be related. For some exampleimplementations, a mapping from the transform size of the current depthto the transform size of the next depth is shown in the following inTable 1.

TABLE 1 Transform partition size setting Transform Size of Current DepthTransform Size of Next Depth TX_4X4 TX_4X4 TX_8X8 TX_4X4 TX_16X16 TX_8X8TX_32X32 TX_16X16 TX_64X64 TX_32X32 TX_4X8 TX_4X4 TX_8X4 TX_4X4 TX_8X16TX_8X8 TX_16X8 TX_8X8 TX_16X32 TX_16X16 TX_32X16 TX_16X16 TX_32X64TX_32X32 TX_64X32 TX_32X32 TX_4X16 TX_4X8 TX_16X4 TX_8X4 TX_8X32 TX_8X16TX_32X8 TX_16X8 TX_16X64 TX_16X32 TX_64X16 TX_32X16

Based on the example mapping of Table 1, for 1:1 square block, the nextlevel transform split may create four 1:1 square sub-transform blocks.Transform partition may stop, for example, at 4×4. As such, a transformsize for a current depth of 4×4 corresponds to the same size of 4×4 forthe next depth. In the example of Table 1, for 1:2/2:1 non-square block,the next level transform split may create two 1:1 square sub-transformblocks, whereas for 1:4/4:1 non-square block, the next level transformsplit may create two 1:2/2:1 sub transform blocks.

In some example implementations, for luma component of an intra codedblock, additional restriction may be applied with respect to transformblock partitioning. For example, for each level of transformpartitioning, all the sub-transform blocks may be restricted to havingequal size. For example, for a 32×16 coding block, level 1 transformsplit creates two 16×16 sub-transform blocks, level 2 transform splitcreates eight 8×8 sub-transform blocks. In other words, the second levelsplitting must be applied to all first level sub blocks to keep thetransform units at equal sizes. An example of the transform blockpartitioning for intra coded square block following Table 1 is shown inFIG. 15 , together with coding order illustrated by the arrows.Specifically, 1502 shows the square coding block. A first-level splitinto 4 equal sized transform blocks according to Table 1 is shown in1504 with coding order indicated by the arrows. A second-level split ofall of the first-level equal sized blocks into 16 equal sized transformblocks according to Table 1 is shown in 1506 with coding order indicatedby the arrows.

In some example implementations, for luma component of inter codedblock, the above restriction for intra coding may not be applied. Forexample, after the first level of transform splitting, any one ofsub-transform block may be further split independently with one morelevel. The resulting transform blocks thus may or may not be of the samesize. An example split of an inter coded block into transform locks withtheir coding order is show in FIG. 16 . In the Example of FIG. 16 , theinter coded block 1602 is split into transform blocks at two levelsaccording to Table 1. At the first level, the inter coded block is splitinto four transform blocks of equal size. Then only one of the fourtransform blocks (not all of them) is further split into foursub-transform blocks, resulting in a total of 7 transform blocks havingtwo different sizes, as shown by 1604. The example coding order of these7 transform blocks is shown by the arrows in 1604 of FIG. 16 .

In some example implementations, for chroma component(s), someadditional restriction for transform blocks may apply. For example, forchroma component(s) the transform block size can be as large as thecoding block size, but not smaller than a predefined size, e.g., 8×8.

In some other example implementations, for the coding block with eitherwidth (W) or height (H) being greater than 64, both the luma and chromacoding blocks may be implicitly split into multiples of min (W, 64)×min(H, 64) and min (W, 32)×min (H, 32) transform units, respectively. Here,in the present disclosure, a “min (a, b)” may return a smaller valuebetween a and b.

FIG. 17 further shows another alternative example scheme forpartitioning a coding block or prediction block into transform blocks.As shown in FIG. 17 , instead of using recursive transform partitioning,a predefined set of partitioning types may be applied to a coding blockaccording a transform type of the coding block. In the particularexample shown in FIG. 17 , one of the 6 example partitioning types maybe applied to split a coding block into various number of transformblocks. Such scheme of generating transform block partitioning may beapplied to either a coding block or a prediction block.

In more detail, the partitioning scheme of FIG. 17 provides up to 6example partition types for any given transform type (transform typerefers to the type of, e.g., primary transform, such as ADST andothers). In this scheme, every coding block or prediction block may beassigned a transform partition type based on, for example, arate-distortion cost. In an example, the transform partition typeassigned to the coding block or prediction block may be determined basedon the transform type of the coding block or prediction block. Aparticular transform partition type may correspond to a transform blocksplit size and pattern, as shown by the 6 transform partition typesillustrated in FIG. 17 . A correspondence relationship between varioustransform types and the various transform partition types may bepredefined. An example is shown below with the capitalized labelsindicating the transform partition types that may be assigned to thecoding block or prediction block based on rate distortion cost:

-   -   PARTITION_NONE: Assigns a transform size that is equal to the        block size.    -   PARTITION_SPLIT: Assigns a transform size that is ½ the width of        the block size and ½ the height of the block size.    -   PARTITION_HORZ: Assigns a transform size with the same width as        the block size and ½ the height of the block size.    -   PARTITION_VERT: Assigns a transform size with ½ the width of the        block size and the same height as the block size.    -   PARTITION_HORZ4: Assigns a transform size with the same width as        the block size and ¼ the height of the block size.    -   PARTITION_VERT4: Assigns a transform size with ¼ the width of        the block size and the same height as the block size.

In the example above, the transform partition types as shown in FIG. 17all contain uniform transform sizes for the partitioned transformblocks. This is a mere example rather than a limitation. In some otherimplementations, mixed transform blocks sizes may be used for thepartitioned transform blocks in a particular partition type (orpattern).

A video block (a PB or a CB, also referred to as PB when not beingfurther partitioned into multiple prediction blocks) may be predicted invarious manners rather than being directly encoded, thereby utilizingvarious correlations and redundancies in the video data to improvecompression efficiency. Correspondingly, such prediction may beperformed in various modes. For example, a video block may be predictedvia intra-prediction or inter-prediction. Particularly in aninter-prediction mode, a video block may be predicted by one or moreother reference blocks or inter-predictor blocks from one or more otherframes via either single-reference or compound-referenceinter-prediction. For implementation of inter-prediction, a referenceblock may be specified by its frame identifier (temporal location of thereference block) and a motion vector indicating a spatial offset betweenthe current block being encoded or decoded and the reference block(spatial location of the reference block). The reference frameidentification and the motion vectors may be signaled in the bitstream.The motion vectors as spatial block offsets may be signaled directly, ormay be itself predicted by another reference motion vector or predictormotion vector. For example, the current motion vector may be predictedby a reference motion vector (of e.g., a candidate neighboring block)directly or by a combination of reference motion vector and a motionvector difference (MVD) between the current motion vector and thereference motion vector. The latter may be referred to as merge modewith motion vector difference (MMVD). The reference motion vector may beidentified in the bitstream as a pointer to, for example, a spatiallyneighboring block or a temporarily neighboring but spatially collocatedblock of the current block.

In some other example implementations, an intra-block copy (IBC)prediction may be employed. In IBC, a current block in the current framemay be predicted using another block in the current frame (rather than atemporally different frame, hence the term “intra”) in combination of ablock vector (BV) for indicating an offset of the location of theintra-predictor or reference block to that of the block being predicted.The location of the coding blocks may be represented by the pixelcoordinates of, e.g., to-left corner relative to the top-left corner ofthe current frame (or slice). The IBC mode, thus use similarinter-prediction concept within a current frame. A BV, for example, maybe predicted by other reference BVs directly or in combination of a BVdifference between a current BV and the reference BV, amanous topredicting MV using reference MV and MV difference in inter-prediction.IBC is useful in providing improved coding efficiency particular forencoding and decoding video frames having screen content with, forexample, significant number of repeating patterns such as textualinformation, where identical textual segments (letters, symbols, words,phases, etc.) appear in different parts of a same frame and can beemployed to predict one another.

In some implementations, IBC may be treated as a separate predictionmode besides a normal intro-prediction mode and a normalinter-prediction mode. As such, a selection of prediction mode of aparticular block may be made and signaled among three differentprediction modes: intra-prediction, inter-prediction, and IBC modes. Inthese implementations, flexibility may be built in each of these modesto optimize coding efficiency in each of these modes. In some otherimplementations, the IBC may be treated as a submode or branch withinthe inter-prediction mode, using similar motion vector determination,referencing and coding mechanisms. In such implementations (integratedinter-prediction mode and IBC mode), the flexibility of the IBC may besomewhat restricted in order to harmonize the general inter-predictionmode and the IBC mode. However, such implementations are less complexwhile can still take advantage of IBC to improve coding efficiency forvideo frames characterized by, for example, screen content. In someexample implementations, with existing pre-specified mechanisms forseparate inter-prediction mode and intra-prediction mode, theinter-prediction mode may be extended to support IBC.

The selection of these prediction modes may be made at various levels,including but not limited to sequence level, frame level, picture level,slice level, CTU level, CT level, CU level, CB level, or PB level. Forexample, for IBC purposes, decision on whether IBC mode is adopted maybe made and signaled at the CTU level. If a CTU is being signaled asadopting the IBC mode, then all coding blocks in the entire CTU may bepredicted by IBC. In some other implementations, the IBC prediction maybe determined at super block (SB) level. Each SB may be slit intomultiple CTUs or divisions in various manners (e.g., quadtreedivisions). Examples are further provided below.

FIG. 18 illustrates an example snapshot of a section of a current framecontaining a plurality of CTUs from a decoder standpoint. Each squareblock such as 1802 represents a CTU. A CTU may be of one of variouspredefined sizes as described in detail above. Each CTU may include oneor more coding blocks (or prediction blocks, for a particular colorchannel). The CTUs shaded with horizontal lines represents those CTUsthat have already been reconstructed. CTU 1804 represents the currentCTU being reconstructed. Within the current CTU 1804, the coding blocksshaded with horizontal lines represent the those blocks that havealready been reconstructed in the current CTU, the coding block 1806shaded with slanted lines is currently being reconstructed, whereas theunshaded coding blocks in the current CTU 1804 are waiting forreconstruction. Other unshaded CTUs are yet to be processed.

The location or offset of the reference block (relative to the currentblock) used for predicting the current coding block in IBC may beindicated by a BV, as shown by the example arrows in FIG. 18 . Forexample, a BV may indicate the location difference in vector formbetween the upper left corners of the reference block (labeled as “Ref”in FIG. 18 ) and the current block. While FIG. 18 is illustrated usingCTUs as the basic IBC units. The underlying principles apply toimplementations where SBs are used as basic IBC units. In suchimplementations, as described in more detail below, each super block maybe divided into multiple CTUs and each CTUs may be further divided intomultiple coding blocks.

As further disclosed in more detail below, depending on a location of areference CTU/SB relative to a current CTU/SB for IBC, the referenceCTU/SB may be referred to as a local CTU/SB or non-local CTU/SB. A localCTU/SB may refer to a CTU/SB that coincides with the current CTU/SB or aCTU/SB that is near the current CTU/SB and has been reconstructed (e.g.,a left neighboring CTU/SB of the current CTU/SB). A non-local CTU/SB mayrefer to a CTU/SB that is further away from the current CTU/SB. Eitheror both of the local CTU/SB and non-local CTU/SB may be searched forreference blocks when performing IBC prediction of a current codingblock. Specific manners in which the IBC is implemented may depend onwhether the reference CTU/SB is local or non-local, as on-chip andoff-chip storage management of reconstructed samples (such as off-chippicture buffer (DPB) and/or on-chip memory) for local or non-localCTU/SB referencing may differ. Reconstructed local CTU/SBs samples, forexample, may be suitable for storage in an on-chip memory of an encoderor decoder for IBC. Reconstructed non-local CTU/SBs samples, forexample, may be stored in off-chip DPB memory.

In some implementations, the location of reconstructed blocks that maybe used as reference blocks for the current coding block 1804 may berestricted. Such restrictions may be a result of various factors and maydepend on whether the IBC is implemented as an integrated part of thegeneral inter-prediction mode, a special extension of theinter-prediction mode, or a separate and independent IBC mode. In someexamples, only the current reconstructed CTU/SB samples may be searchedfor identify IBC reference block. In some other examples, the currentreconstructed CTU/SB samples and another neighbor reconstructed CTU/SBsamples (e.g., the left neighboring CTU/SB) may be available forreference block search and selection, as shown by the thick dotted frame1808 of FIG. 18 . For such implementations, only local reconstructedCTU/SB samples may be used for IBC reference block search and selection.In some other examples, certain CTU/SB may not be available for IBCreference block search and selection for various other reasons. Forexample, the CTU/SBs 1810 marked with crosses in FIG. 18 at may not beavailable for search and selection of reference blocks for the currentblock 1804, as they may be used for special purposes (e.g., wave frontparallel processing) as described further below.

In some implementations, restrictions as to the already-reconstructedCTU/SBs that are allowed to be used to provide IBC reference blocks orreference samples may result from adoption of parallel decoding, wheremore than one coding blocks are being decoded simultaneously. An exampleis shown in FIG. 19 , where each square represents a CTU/SB. Paralleldecoding may be implemented, in which a plurality of CTU/SBs in a numberof consecutive rows and every other column (every two columns) may bereconstructed in parallel processing, as shown by the CTU/SBs shadedwith slanted lines in FIG. 19 . Other CTU/SBs shaded with horizontallines have already been reconstructed, and the unshaded CTU/SBs are theones that are yet to be constructed. With such parallel processing, fora currently parallel processed CTU/SB having its top-left coordinatebeing (x₀, y₀), reconstructed samples at (x, y) can be accessed forpredicting the current CTU/SB in IBC only if the vertical coordinate yis less than y₀ and horizontal coordinate x is less x₀+2(y₀−y), as such,the already constructed CTU/SB shaded with horizontal line may beavailable as reference for the parallelly processed current blocks.

In some implementations, write-back delay of immediately reconstructedsamples into off-chip DPB may place further restrictions on the CTU/SBsthat may be used to provide IBC reference samples for a current block,particularly when off-chip DPB is used for holding IBC referencesamples. An example is shown in FIG. 20 , where additional restrictionsmay be applied on top of those shown FIG. 19 . Specifically, to allowhardware writing back delay, immediate reconstructed areas may not beaccessed by IBC prediction for search and selection of reference blocks.The number of restricted or prohibited immediate reconstructed areas canbe 1 n CTU/SBs (n being a positive integer). As such, on top of theparticular parallel processing restriction of FIG. 19 , if thecoordinate of one current CTU/SB's top-left position is (x₀, y₀), theprediction at position (x, y) can be accessed by IBC, if verticalcoordinate y is less than y₀ and horizontal coordinate is less thanx₀+2(y₀−y)−D, where D denotes the number of immediate reconstructed area(e.g., to the left of the current CTU/SB) that are restricted/prohibitedfor us as IBC reference. FIG. 20 illustrates such additional CTU/SBsthat are restricted out as IBC reference samples for D=2. Theseadditional CTU/SBs that are not available as IBC reference are indicatedby the inverted slanted-line shading.

In some implementations, also described in further detail below, boththe local and non-local CTU/SBs search areas may be used for IBCreference block search and selection. In addition, when on-chip memoryis used, some of the restrictions as to availability of analready-constructed CTU/SB as IBC reference with respect to write backdelays may be relaxed or removed. In some further implementations, themanner in which the local CTU/SBs and non-local CTU/SBs are used, whenin co-existence, may differ, due to difference in, for example,management of buffering of the reference blocks using either on-chip oroff-chip memories. These implementations are described in further detailin the disclosure below.

In some implementations, IBC may be implemented as an extension ofinter-prediction mode, treating a current frame as a reference frame ininter-prediction mode such that blocks within the current frame may beused as prediction reference. Such IBC implementations thus may follow acoding path for inter prediction, even although the IBC process onlyinvolves the current frame. In such an implementation, the referencingstructure of inter-prediction mode may be adapted for IBC, where therepresentation of the addressing mechanism to the reference samplesusing BVs can be analogous to motion vectors (MVs) in inter-prediction.As such, IBC may be implemented as a special inter prediction mode,relying on similar or identical syntax structure and decoding processesas inter-prediction mode based on the current frame as a referenceframe.

In such implementations, as IBC may be treated as an inter-predictionmode, an intra-only predicted slice has to become a predicted slice forallowing the usage of IBC. In other words, an intra-only predictionslice would not be inter-predicted (as intra prediction mode would notinvoke any inter-prediction processing path) and thus IBC would not beallowed for prediction in such intra-only slice. When IBC is applicable,the coder would extend the reference picture lists by one entry for thepointer to the current picture. The current picture thus may take up toone picture-sized buffer of the shared decoded picture buffer (DPB). Thesignaling for use of IBC may be implicit in the choice of referenceframe in the inter-prediction mode. For example, when the selectedreference picture points to the current picture, the coding unit wouldemploy IBC with inter-prediction-like coding path with special IBCextensions if needed and available. In some specific implementations,reference samples within the IBC process may not be loop filtered beforebeing used for prediction, in contrast to regular inter prediction.Further, the corresponding reference current picture may be a long-termreference frame as it would be near next frames to be encoded ordecoded. In some implementations, to minimize the memory requirement,the coder may immediately release the buffer after reconstructing thecurrent picture. The coder may fill a filtered version of thereconstructed picture back into the DPB as a short-term reference whenit becomes reference picture for later frames in true inter-prediction,even though it may be unfiltered when being used for the IBC.

In the example implementations above, even though the IBC may be a mereextension of the inter-prediction mode, the IBC may be treated withseveral special procedures that may depart from normal inter-prediction.For example, the IBC reference samples, again, may be unfiltered. Inother words, the reconstructed samples before the in-loop filteringprocesses, including deblocking filtering, Sample Adaptive Offset (SAO)filtering, Cross-Component Sample Offset (CCSO) filtering, and the like,may be used for IBC prediction, whereas the normal inter prediction modeemploy filtered samples for prediction. For another example, no lumasample interpolation for IBC may not be performed, and chroma sampleinterpolation may only be necessary when the chroma BV is a non-integerwhen derived from the luma BV. For yet another example, when the chromaBV is non-integer, and the reference block for IBC is near the boundaryof an available region for IBC reference, the surrounding reconstructedsamples may be outside of the boundary to perform chroma interpolation.BVs pointing to a single next-to-border line are not possible to avoidsuch cases.

In such implementations, prediction of a current block by IBC may reusethe prediction and coding mechanism of the inter-prediction process,including using a reference BV to predict a current BV and, for example,an additional BV difference. In some specific implementations, however,luma BVs may be implemented in integer resolution rather than fractionalprecision as in MV for regular inter prediction.

In some implementations, all CTUs and SBs indicated with horizontalshading lines in FIG. 18 may be used for search and selection of IBCreference block except for the two CTUs on the right and above thecurrent CTU (indicated by the crosses in FIG. 18 ) for allowingWavefront Parallel Processing (WPP), shown as 1810 in FIG. 18 . As such,almost the whole already reconstructed area of the current picture, withsome exceptions for parallel processing purposes.

In some other implementations, the areas from which IBC reference blocksmay be searched and selected may be restricted to local CTU/SBs. Oneexample is indicated by the thick dotted frame 1808 of FIG. 18 . In suchan example, the CTU/SB to the left of the current CTU may serve as thereference sample area for IBC at the beginning of the current CTU'sreconstruction process. When using such local reference areas, insteadof allocating additional external memory space in the DPB, on-chipmemory space may be allocated for keeping the local CTU/SB for IBCreference. In some implementations, a fixed on-chip memory may be usedfor IBC, thereby reducing a complexity of implementing IBC in hardwarearchitectures. As such, a dedicated IBC mode independent of normalinter-prediction may be implemented for utilization of on-chip memory,rather than being implemented as a mere extension of theinter-prediction mode.

For example, the fixed on-chip memory size for storing local IBCreference samples, e.g., the left CTU or SB, may be 128×128 for eachcolor component. In some implementations, a maximum CTU size may alsoalso 128×128. In such cases, the reference sample memory (RSM) can holdsamples have a size of a single CTU. In some other alternativeimplementations, the CTU size may be less. For example, the CTU size maybe 64×64. As such, the RSM may hold multiple (4, in this example case)CTUs simultaneously. In yet some other implementations, the RSM may holdmultiple SBs, each SB may include one or more CTUs, and each CTUs mayinclude multiple coding blocks.

In some implementations of local on-chip IBC referencing, the on-chipRSM hold one CTU and may implement a continuous update mechanism forreplacing the reconstructed samples of the left neighboring CTU with thereconstructed samples of the current CTU. FIG. 21 illustrates asimplified example for the such continuous RSM update mechanism at fourintermediate times during the reconstruction process. In the example ofFIG. 21 , the RSM has a fixed size that holds one CTU. The CTU mayinclude an implicit division. For example, the CTU may be implicitlydivided into four disjoining areas (e.g., quadtree division). Each areamay include multiple coding blocks. The CTU may be 128×128 in size,whereas each of the example areas or divisions may be 64×64 in size forthe example quadtree division. The areas/divisions of the RSM shadedwith horizontal lines in each of the intermediate times holdcorresponding reconstructed reference samples of the left-neighboringCTU, and the areas/divisions shaded with vertical lines gray holdscorresponding reconstructed reference samples of the current CTU. Thecoding block of the RSM shaded with slanted lines represents the currentcoding block within the current area being coded/decoded/reconstructed.

At the first intermediate time, representing the beginning of thecurrent CTU reconstruction, the RSM may include reconstructed referencesamples of the left neighboring CTU only for each of the four exampleareas, as shown by 2102. In the other three intermediate times, thereconstruction process has gradually replaced reconstructed referencesamples of the left neighboring CTU with the current CTU's reconstructedsamples. A reset of an area/division of 64×64 in the RSM occurs when thecoder processes the first coding block of that area/division. At thetime of resetting an area of the RSM, that area is considered blank andis considered not holding any reconstructed reference samples for IBC(in other words, that area of RSM is not ready for use as IBC referencesamples). As the corresponding current coding blocks in that area areprocessed, the corresponding blocks in the RSM are filed withreconstructed samples of the corresponding blocks of the current CTU tobe used as reference samples for IBC for next current blocks, as shownin FIG. 21 for intermediate times 2104, 2106, and 2108. Once all codingblocks are processed corresponding to an area/division of the RSM, thatentire area is filled with reconstructed samples of these current codingblocks as IBC reference samples, as shown by the areas fully shaded withvertical lines in FIG. 21 at various intermediate times. As such, inintermediate times 2104 and 2106, some areas/divisions in the RSM holdIBC reference samples from neighboring CTU, some other areas/divisionsentirely hold reference samples from the current CTU, whereas someareas/divisions partially hold reference samples from the current CTUand partially blank (not used for IBC reference as a result of the resetprocess described above). As the final area (e.g., the bottom-rightarea) is being processed, all other three areas would hold reconstructedsamples of the current CTU as reference samples for IBC whereas the lastarea/division partially holds reconstructed samples of correspondingcoding blocks in the current CTU and is partially blank, until the finalcoding block of the CTU is reconstructed, at which time the entire RSMhold the reconstructed samples of the current CTU and the RSM is readyfor use for the next CTU if also coded in IBC mode.

FIG. 22 illustrates the above continuous update implementation of theRSM spatially at a particularly intermediate time, i.e., the leftneighboring CTU and the current CTU with the current coding block (theblock shaded by slanted shading lines) are both shown. The correspondingreconstructed samples for these two CTUs that are in the RSM and areeffective as IBC reference samples for the current coding block areshown by the horizontal and vertical shading lines. At the particularreconstruction time in this example, the processing has replaced, in theRSM, the samples covered by the unshaded area in the left neighboringCTU with the areas of the current CTU shaded by vertical shading lines.The remaining effect samples from the neighboring CTU is shown ashorizontal-line shading.

In the example implementation above, the RSM is implemented to containone CTU when the fixed RSM size is the same as the CTU size. In someother implementations, where CTU size is smaller, the RSM may containmore than a single CTU. For example, the size of a CTU may be 32×32whereas the fixed RSM size may be 128×128. As such, the RSM may holdsamples of 16 CTUs. Following the same underlying RSM updatingprinciples described above, the RSM may hold 16 neighboring CTUs of acurrent 128×128 patch prior to being reconstructed. As soon as theprocessing of the first coding block of the current 128×128 patchcommences, the first 32×32 region of the RSM initially filled withreconstructed samples of one neighboring CTU may updated as describedabove for an RSM holding a single CTU. The remaining fifteen 32×32regions contain 15 neighboring CTUs as reference samples for IBC. Oncethe CTU corresponding to the first 32×32 region of the current 128×128patch being decoded is reconstructed, the first 32×32 region of the RSMis updated with the reconstructed samples of this CTU. Then the CTUcorresponding to the second 32×32 region of the current 128×128 patchmay be processed and eventually updated with the reconstructed samples.This process continues until the sixteen 32×32 regions of the RSMcontain reconstructed samples of the current 128×128 patch (all 15CTUs). The decoding process then move on to the next 128×128 patch.

In some other implementations, as an expansion of FIG. 21 ad 22, the RSMmay hold a set of neighboring CTUs. One current CTU is processed at atime, the RSM portion holding the furthest neighboring CTU is updated inthe manner described above with the reconstructed current CTU. For thenext current CTU, again, the furthest neighbor CTU in the RSM is updatedand replaced. As such, the multiple CTUs held in the fixed size RSMupdate as a moving window of neighboring CTUs for IBS.

A further specific example implementation of local IBC using on-chip RSMis shown in FIG. 23 . In this example, the largest block size for IBCmode may be limited. For example, the largest IBC block may be 64×64.The on-chip RSM may be configured with a fixed size, e.g., 128×128,corresponding to a superblock (SB). The RSM implementation of FIG. 23use similar underlying principle of the implementation of FIG. 21 andFIG. 22 . In FIG. 23 , the RSM may hold multiple neighboring and/orcurrent CTU as IBC reference samples. In the example of FIG. 23 , the SBmay be quadtree split. Correspondingly, the RSM may be quadtree split in4 regions or units each being 64×64. Each of these areas may hold one ormore coding blocks. Alternatively, each of these areas may hold one ormore CTUs and each CTUs may hold one or more coding blocks. The codingorder of the quadtree areas may be predefined. For example, the codingorder may be top-left, top-right, bottom left, to bottom right. Thequadtree splitting of the SB of FIG. 23 is merely one example. In someother alternative implementations, SB may be split following any otherscheme. The RSM updating implementations for local IBC described hereinapplies to those alternative splitting schemes.

In such local SBC implementations, the local reference blocks that maybe used for SBC prediction may be limited. For example, it may berequired that the reference block and the current block should be in thesame SB row. Specifically, the local reference block may only be locatedin the current SB or one SB on the left to the current SB. Examplecurrent blocks as being predicted in SBC by another allowed coding blockare shown by the dashed arrows in FIG. 23 . When the current SB or theleft SB are used for SBC reference, the reference sample updatingprocedure in the RSM may follow the reset procedure described above. Forexample, when any of the 64×64 unit reference sample memory begins toupdate with the reconstructed samples from the current SB, the previousstored reference samples (from the left SB) in the whole 64×64 unit aremarked as unavailable for generating IBC prediction samples and it isgradually updated with reconstructed samples of the current blocks.

FIG. 23 shows 5 example states of the RSM during local IBC decoding of acurrent SB in panel 2302. Again, the areas of the RSM shaded withhorizontal lines in each of the example states hold correspondingreference samples of the corresponding quadtree area of theleft-neighboring SB, and the areas/divisions shaded with vertical linesgray holds corresponding reference samples of the current SB. The codingblock of the RSM shaded with slanted lines represents the current codingblock within the current quadtree area being coded/decoded. At thebeginning of coding of each current SB, the RSM stores samples of theprevious coded SB (RSM state (0) of FIG. 23 ). When the current block islocated in one of the four 64×64 quadtree areas in the current SB, thecorresponding region in the RSM is reset and used to store the samplesof current 64×64 coding region. In this way, the samples in each 64×64quadtree area of the RSM are gradually updated by the samples in thecurrent SB (state (1)-state (3)). When the current SB has been codedcompletely, the entire RSM is filled with all the samples of the currentSB (state (4)).

Each of the 64×64 area in panel 2302 of FIG. 23 is labeled with aspatial coding sequence number. Sequence 0-3 represents the four 64×64quadtree areas of the left neighbor SB, whereas sequence 4-7 representsthe four 64×64 quadtree areas of the current SB Panel. In FIG. 23 ,panel 2304 further illustrates the corresponding spatial distribution inthe left neighboring and current SBs of the reference samples in the128×28 RSM, for RSM state (1), state (2), and state (3) of panel 2302 ofFIG. 23 . The shaded areas without crosses represents areas withreconstructed samples in the RSM. The shaded areas with crossesrepresent areas with reconstructed samples of the left SB in the RSMbeing reset (and thus unavailable as reference samples for local SBC).

The coding order of the 64×64 areas and corresponding RSM update ordermay follow either a horizontal scan (as shown above in FIG. 23 ) orvertical scan. Horizontal scan starts from top-left, to top right,bottom left, and bottom right. Vertical scan starts from top-left, tobottom left, to top right, and to bottom left. The left neighbor SB andcurrent SB reference sample update processes for the horizontal scan andvertical scan are respectively illustrated in panel 2402 and 2404 ofFIG. 24 for comparison when the each of the four 64×64 areas of thecurrent SB is being reconstructed. In FIG. 24 , the 64×64 areas shadedwith horizontal lines without crosses represent areas with samplesavailable for SBC. The areas shaded with horizontal lines with crossesrepresent the areas of the left neighboring SB that have been updated tothe corresponding reconstructed samples of the current SB. The unshadedregions represent unprocessed regions of the current SB. The blocksshaded with slanted lines represent the current coding block beingprocessed.

As shown in FIG. 24 , depending on the location of the current codingblock relative to the current SB, the following restrictions withrespect to reference block for IBC may apply.

If the current block falls into the top-left 64×64 area of the currentSB, then in addition to the already reconstructed samples in the currentSB, it can also refer to the reference samples in the bottom-right,bottom-left and top-right 64×64 block of the left SB, as shown in 2412(for horizontal scan) and 2422 (for vertical scan) of FIG. 24 .

If the current block falls into the top-right 64×64 block of the currentSB, then in addition to the already reconstructed samples in the currentSB, if luma sample located at (0, 64) relative to the current SB has notyet been reconstructed, the current block can also refer to thereference samples in the bottom-left 64×64 block and bottom-right 64×64block of the left SB (2414 of FIG. 24 ). Otherwise, the current blockcan also refer to reference samples in bottom-right 64×64 block of theleft SB (2426 of FIG. 24 ) for SBC.

If the current block falls into the bottom-left 64×64 block of thecurrent SB, then in addition to the already reconstructed samples in thecurrent SB, if luma location (64, 0) relative to the current SB has notyet been reconstructed, the current block can also refer to thereference samples in the top-right 64×64 block and bottom-right 64×64block of the left SB (2424 of FIG. 24 ). Otherwise, the current blockcan also refer to the reference samples in the bottom-right 64×64 blockof the left SB (2416 of FIG. 24 ) for SBC.

If the current block falls into the bottom-right 64×64 block of thecurrent SB, it can only refer to the already reconstructed samples inthe current SB (2418 and 2428 of FIG. 24 ) for SBC.

As described above, in some example implementations, either one of orboth local and non-local-based CTU/SBs may be used for IBC referenceblock search and selection. In addition, when on-chip RSM is used forlocal reference, some of the restrictions as to availability of analready-constructed CTU/SB as IBC reference with respect to write backdelay may be relaxed or removed. Such implementations may be appliedregardless of whether parallel decoding is employed or not.

Example implementations of the local and non-local reference CTU/SBsthat may be used for IBC are shown in FIG. 25 , where, again, eachsquare represents a CTU/SB. The CTU/SBs shaded with slanted linesrepresent current CTU/SBs (Labeled as “0”), whereas the CTU/SBs shadedwith horizontal lines (labeled as “1”), vertical lines (labeled as “2”),and inverted-slanted lines (labeled as “3”) representalready-constructed areas. The unshaded CTU/SBs represent the areas thatare yet to be reconstructed. It is assumed that the parallel decodingsimilar to that of FIG. 19 and FIG. 20 is used. The CTU/SBs shaded withvertical lines (“2”) and inverted-slanted lines (“3”) represent exampleareas normally restricted out as SBC references for the current CTU/SBsdue to write back delay to DPB when only off-chip memory is used for SBCreferencing (see FIG. 20 ). When on-chip RSM is used, then one or moreof the restricted areas of FIG. 20 may be referenced directly from theRSM and thus may not need be restricted out. The number of therestricted areas that can now be accessed via RSM for IBC reference maydepending on the size of the RSM. In the example of FIG. 25 , it isassumed that the RSM can hold one CTU/SB and employ the RSM updatemechanism described above. As such, one of the two sets of neighboringCTU/SB shaded in inverted-slanted lines of FIG. 20 , labeled as “3”, maybe available for local reference. The RSM then holds samples from theleft CTU/SBs and the current CTU/SBs. Thus, in the example of FIG. 25 ,the search area available for non-local SBC reference blocks includesthe CTU/SB labeled as “1” (search area 1, or SA1), the scan areaavailable for local SBC reference blocks includes the CTU/SB labeled as“2” and “0” (SA2), and the restricted-out area for SBC reference blocksinclude the CTU/SB labeled as “3” due to writeback delay. In some otherimplementations, with sufficient on-chip RSM size that can hold theentire restricted CTU/SBs, then all these potentially restricted areasare includable in the RSM for local referencing.

FIG. 26 further shows further restriction on reference coding blocksthat may be used in IBC for predicting a current coding block when bothlocal and non-local reference search is allowed and enabled. In FIG. 26, again, each square represents a CTU/SB. The CTU/SBs shaded withhorizontal lines represent already-constructed CTU/SBs. The unshadedCTU/SBs represent the areas that are yet to be reconstructed. TheCTU/SBs with inverted-slanted shading lines are the ones that are notallowed as IBC reference (here only the current CTU/SB is shown as beingallowed for IBC referencing, however, the underlying principles apply tothe situation where only the first one of the two CTU/SBs withinverted-slanted shading lines is disallowed, as in FIG. 25 ). Thecoding block with slanted shading lines is the current coding block.Coding blocks A, B, and C are potential reference blocks for IBC for thecurrent coding block. Other shaded coding blocks in the current CUT/SBhave already been constructed. In this implementation, reference codingblock B is allowed because it entirely sits outside of the restrictedarea and in SA2 (local search area), and has been reconstructed already.Coding block C is also allowed because it entirely sits outside of therestricted area and in SA1 (non-local search area), and has beenreconstructed already. Coding block A is not allowed for use asprediction block since it overrides SA1 and SA2. In other words,reference coding block overriding both SA1 and SA2 may not be allowed,as the treatment for IBC for SA1 and SA2 may be different and nor easilyharmonized.

Turning to coding of the block vectors (BVs) in IBC, in some exampleimplementations, processes similar to those specified for interprediction may be employed, but use more simplistic rules for BVprediction candidate list construction may be used. For example, thecandidate list construction for some inter prediction implementationsmay consist of five spatial, one temporal, and six history-basedcandidates. In such inter-prediction, multiple candidate comparisons maybe performed for history-based candidates, in order to avoid duplicateentries in the final candidate list. Additionally, the list constructionmay include pairwise averaged candidates. In some exampleimplementations of BV prediction, the IBC list construction process mayconsider a number of (e.g., two) spatial neighbors' BV and a number of(e.g., five) history-based BVs (HBVP), where only the first HBVP maycompare with spatial candidates when being added to the candidate list.While the regular inter-prediction may use two different candidatelists, one for the merge mode and the other for the regular mode, thecandidate list in IBC may be used for both cases with respect to BV.However, the merge mode may use up to six candidates of the list,whereas the regular mode uses only the first two candidates. In someexample implementations, the block vector difference (BVD) coding mayemploy the motion vector difference (MVD) process, resulting in a finalBV of any magnitude. The reconstructed BV may point to an area outsideof the reference sample area, requiring a correction by removing theabsolute offset for each direction using the modulo operation with theRSM's width and height.

In the implementations above where either one of or both local andnon-local IBC referencing is used, loop filters may be utilized undercertain circumstances. For example, when non-local based IBC searchrange is used (with or without local-based IBC search range), forexample for one picture, the loop filters may be disabled for the samepicture in IBC. On the other hand, if only local based IBC search rangeis used (without non-local based IBC search range), loop filters may beused for the same picture. The loop filters may include but are notlimited to deblocking filter, Constrained Directional Enhancement Filter(CDEF), Sample Adaptive Offset (SAO) filtering, Cross-Component SampleOffset (CCSO) filter, and the Loop Restoration filter (LR). In such amanner, a second picture buffer dedicated for enabling IBC can beavoided.

Turning now to IBC related signaling, in some implementations, for thecurrent block, a flag used for indicating whether IBC is enabled or notfor current block is first transmitted in bitstream. Such flag may besignaled at higher level such as CTU, CU, sequence, slice, or picturelevels. Then, if the current block is in IBC mode (either as a separatemode from inter-prediction mode, or as integral part of theinter-predication mode), a reference block may be searched and thecorresponding BV may be determined by the encoder. For BV prediction,the BV difference may be derived in the decoder by subtracting thepredicted BV from the current BV, and then BV difference may beclassified into multiple types (e.g., 4 types) according to thehorizontal and vertical component of the BV difference value. The BVdifferent type information may be further signaled in the bitstream, andthe BV difference value of the two (horizontal and vertical) componentsmay be signaled afterwards. In some example implementations, a set ofhigh-level syntax flags are further included in the bitstream and usedto indicate the allowable local and or non-local reference range(s) ofIBC prediction. Such a set of flags can be signaled at various levels,e.g., at CTU, CU, sequence, slice, or picture level.

For example, a syntax flag, referred to as global_ibc_flag, may be usedto turn on/off the non-local based region while another syntax flag,referred to as local_ibc_flag, may be used to turn on/off the localbased region for IBC prediction. These two syntax flags may becontrolled independent of each other. In other words, these flags mayhave any combination of flag values. Each of these flags may be signaledat the same of different levels. In one example, when both flags areturned off, effectively IBC is disabled. In this case, where thenon-local IBC flag and local IBC flag are independently signaled for aparticular level, the enabling flag for IBC at that level (such aspicture level or sequence level) described above need not be signaled inthe bitstream.

In some example implementations, the non-local IBC syntax flag,global_ibc_flag, and the local IBC syntax flag, local_ibc_flag, may beconfigured with certain dependency. For example, the non-localglobal_ibc_flag may be signaled first. Depending on its value, thelocal_ibc_flag may be signaled or inferred. When global_ibc_flag isequal to 0 (meaning not used), local_ibc_flag may be inferred to be 1(meaning used) in conjunction with that IBC is signaled as being used by(e.g., the high-level IBC enabling syntax above), instead of beingsignaled. In this example, one or both of the local and nonlocal flagsare signaled only when IBC enabled flag is turned on. Otherwise, none ofthese two flags need be signaled.

In some example implementations, when non-local based IBC search rangeis used, for example for one picture, the loop filters will be disabledfor the same picture. On the other hand, if only local based IBC searchrange is used (but not non-local based IBC search range), loop filtersmay be used for the same picture. Therefore, enabling flag for loopfilters in IBC are signaled on condition that the IBC is used andnon-local based IBC search range is not used. In other words, a loopfilter enabling flag may be signaled if the other flags above indicatethat non-local based IBC is not used. The loop filter enabling flagwould indicate whether local-based IBC should invoke loop filters ornot. Otherwise, when no IBC is used or only non-local IBC is used, theloop filtering is inferred to be disabled and the loop filter enablingflags need not be signaled. Specifically, the signaling of use of loopfilters may be conditioned on the value of global_ibc_flag. Whenglobal_ibc_flag is on (meaning non-local IBC reference search is used),the enabling flag for loop filters for the picture may be inferred to be0 (or be turned off) and need not be signaled.

In the manner described above, the various flags or syntax elementsabove, alone or in various combinations, may indicate or signal an IBCreferencing mode for the current block. An IBC referencing moderepresents how the local search areas and the non-local search areas areaccessible for IBC prediction blocks. For example, the combination ofthese flags or syntax elements may indicate that only the CTUs or SBsamong the local search area are available for IBC referencing, hence thelocal-referencing IBC mode. For another example, the combination ofthese flags or syntax elements may indicate that only the CTUs or SBs inthe non-local search areas are available for IBC referencing, hence thenon-local IBC referencing mode. For yet another example, the combinationof these flags or syntax elements may indicate that the CTUs or SBs inboth the local and non-local search areas are available for IBCreferencing, hence the local-and-non-local-referencing IBC mode. Adecoder may extract these syntax elements either independently or basedtheir dependency as described above to determine the IBC referencingmode, thereby obtaining information as to determine the search areas forIBC reference blocks.

FIG. 27 shows a flow chart 2700 of an example method following theprinciples underlying the implementations above for IBC. The examplemethod flow starts at 2701. In S2710, at least one syntax element isextracted from the video stream, the at least one syntax element beingassociated with an intra block copy (IBC) prediction of the video block.In S2720, an IBC referencing mode for the IBC prediction of the videoblock is determined, the IBC referencing mode may include one of no-IBCmode, a local-referencing IBC mode, a non-local-referencing IBC mode,and a local-and-non-local-referencing IBC mode. In S2730, reconstructedsamples of the video block are generated from the video stream based onthe IBC referencing mode. The example method flow ends at S2799.

In the embodiments and implementation of this disclosure, any stepsand/or operations may be combined or arranged in any amount or order, asdesired. Two or more of the steps and/or operations may be performed inparallel. Embodiments and implementations in the disclosure may be usedseparately or combined in any order. Further, each of the methods (orembodiments), an encoder, and a decoder may be implemented by processingcircuitry (e.g., one or more processors or one or more integratedcircuits). In one example, the one or more processors execute a programthat is stored in a non-transitory computer-readable medium. Embodimentsin the disclosure may be applied to a luma block or a chroma block. Theterm block may be interpreted as a prediction block, a coding block, ora coding unit, i.e. CU. The term block here may also be used to refer tothe transform block. In the following items, when saying block size, itmay refer to either the block width or height, or maximum value of widthand height, or minimum of width and height, or area size (width*height),or aspect ratio (width:height, or height:width) of the block.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 28 shows a computersystem (2800) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 28 for computer system (2800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2800).

Computer system (2800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2801), mouse (2802), trackpad (2803), touchscreen (2810), data-glove (not shown), joystick (2805), microphone(2806), scanner (2807), camera (2808).

Computer system (2800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2810), data-glove (not shown), or joystick (2805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2809), headphones(not depicted)), visual output devices (such as screens (2810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2820) with CD/DVD or the like media (2821), thumb-drive (2822),removable hard drive or solid state drive (2823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2800) can also include an interface (2854) to one ormore communication networks (2855). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CAN bus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general-purpose data ports or peripheral buses (2849) (such as,for example USB ports of the computer system (2800)); others arecommonly integrated into the core of the computer system (2800) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2800) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2840) of thecomputer system (2800).

The core (2840) can include one or more Central Processing Units (CPU)(2841), Graphics Processing Units (GPU) (2842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2843), hardware accelerators for certain tasks (2844), graphicsadapters (2850), and so forth. These devices, along with Read-onlymemory (ROM) (2845), Random-access memory (2846), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(2847), may be connected through a system bus (2848). In some computersystems, the system bus (2848) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (2848), or through a peripheral bus (2849). In anexample, the screen (2810) can be connected to the graphics adapter(2850). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (2841), GPUs (2842), FPGAs (2843), and accelerators (2844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2845) or RAM (2846). Transitional data can also be stored in RAM(2846), whereas permanent data can be stored for example, in theinternal mass storage (2847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2841), GPU (2842), massstorage (2847), ROM (2845), RAM (2846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As a non-limiting example, the computer system having architecture(2800), and specifically the core (2840) can provide functionality as aresult of processor(s) (including CPUs, GPUs, FPGA, accelerators, andthe like) executing software embodied in one or more tangible,computer-readable media. Such computer-readable media can be mediaassociated with user-accessible mass storage as introduced above, aswell as certain storage of the core (2840) that are of non-transitorynature, such as core-internal mass storage (2847) or ROM (2845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit

HDR: high dynamic rangeSDR: standard dynamic range

WET: Joint Video Exploration Team

MPM: most probable mode

WAIP: Wide-Angle Intra Prediction CU: Coding Unit PU: Prediction UnitTU: Transform Unit CTU: Coding Tree Unit PDPC: Position DependentPrediction Combination ISP: Intra Sub-Partitions SPS: Sequence ParameterSetting PPS: Picture Parameter Set APS: Adaptation Parameter Set VPS:Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive LoopFilter SAO: Sample Adaptive Offset CC-ALF: Cross-Component Adaptive LoopFilter CDEF: Constrained Directional Enhancement Filter CCSO:Cross-Component Sample Offset LSO: Local Sample Offset LR: LoopRestoration Filter AV1: AOMedia Video 1 AV2: AOMedia Video 2 RPS:Reference Picture Set DPB: Decoded Picture Buffer

MMVD: Merge Mode with Motion Vector Difference

IntraBC or IBC: Intra Block Copy BV: Block Vector BVD: Block VectorDifference RSM: Reference Sample Memory

What is claimed is:
 1. A method for reconstructing a video block in avideo stream, comprising: receiving the video stream; extracting atleast one syntax element from the video stream, the at least one syntaxelement being associated with intra block copy (IBC) prediction of thevideo block; determining an IBC referencing mode for the IBC predictionof the video block, the IBC referencing mode comprises one of no-IBCmode, a local-referencing IBC mode, a non-local-referencing IBC mode,and a local-and-non-local-referencing IBC mode; and generatingreconstructed samples of the video block from the video stream based onthe IBC referencing mode.
 2. The method of claim 1, wherein the videoblock belongs to a current IBC prediction unit comprising a plurality ofvideo blocks.
 3. The method of claim 2, wherein, for thenon-local-referencing IBC mode, a reference block for the IBC predictionof the video block comprises reference samples in reconstructedintra-frame areas that are non-neighbors to the current IBC predictionunit in a coding direction of the current IBC prediction unit.
 4. Themethod of claim 2, wherein, for the local-referencing IBC mode, areference block for the IBC prediction of the video block comprisesreference samples in a predefined set of neighboring units of thecurrent IBC prediction unit or video blocks already-reconstructed in thecurrent IBC prediction unit.
 5. The method of claim 4, wherein thepredefined set of neighboring units comprise a single left neighboringunit of the current IBC prediction unit.
 6. The method of claim 4,wherein, for the local-referencing IBC mode, reference samples for theIBC prediction are maintained in an on-chip reference sample memory(RSM) of a fixed size.
 7. The method of claim 6, wherein the fixed sizeof the RSM corresponds to a size of one IBC prediction unit.
 8. Themethod of claim 7, wherein: first portions of the RSM comprisecorresponding samples of the video blocks already-reconstructed in thecurrent IBC prediction unit; and second portions of the RSM comprisecorresponding reconstructed samples from the predefined set ofneighboring units.
 9. The method of claim 8, further comprisingreplacing reconstructed samples of the neighboring units in the RSMcorresponding to the video block in the current IBC prediction unit withthe reconstructed samples of the video block.
 10. The method of claim 6,wherein: the current IBC prediction unit is split into a predefined setof divisions; the video block is a first coding block to bereconstructed of a current division among the predefined set ofdivisions; and the method further comprises resetting a division of theRSM corresponding to the current division as being unavailable for IBCreferencing prior to reconstruction of the video block.
 11. The methodof claim 2, wherein the at least one syntax element comprises a firstflag for indicating that local IBC referencing is enabled when being setand a second flag for indicating that non-local referencing IBC isenabled when being set.
 12. The method of claim 11, further comprising:in response to the first flag being set and the second flag not beingset, determining that the IBC referencing mode is the local-referencingIBC mode; in response to the second flag being set and the first flagnot being set, determining that the IBC referencing mode is thenon-local-referencing IBC mode; in response to both the first flag andthe second flag not being set, determining that the IBC referencing modeis the local-and-non-local-referencing IBC mode; and in response to boththe first flag and the second flag not being set, determining that theIBC referencing mode is the no-IBC mode.
 13. The method of claim 11,where the first flag and the second flag are signaled in the videostream at a coding block level, coding unit level, a coding tree unitlevel, a slice level, a picture level, or a sequence level.
 14. Themethod of claim 2, wherein the at least one syntax element comprises afirst flag for indicating whether IBC is used for the video block. 15.The method of claim 14, further comprising: in response to the firstflag indicating that IBC is not used for the video block, determiningthat the IBC referencing mode is the no-IBC mode.
 16. The method ofclaim 15, further comprising: in response to the first flag indicatingthat IBC is used for the video block, further extracting, as part of theat least one syntax element, a second flag for indicating whethernon-local IBC referencing is used; in response to the second flagindicating that non-local IBC referencing not used, inferring that theIBC referencing mode for the video block is the local-referencing IBCmode.
 17. The method of claim 16, further comprising: in response to thesecond flag indicating that non-local IBC referencing is used, furtherextract, as part of the at least one syntax element, a third flag forindicating whether local-IBC referencing is used; in response to thethird flag indicating that local-IBC referencing is used, determiningthat the IBC referencing mode is the local-and-non-local-referencing IBCmode; and in response to the third flag indicating that local-IBCreferencing is not used, determining that the IBC referencing mode isthe non-local-referencing IBC mode.
 18. The method of claim 1, wherein:a loop filtering process is enabled when the IBC referencing mode is thelocal-referencing IBC mode; and the loop filtering process is disabledwhen the IBC referencing mode is the non-local-referencing IBC mode orthe local-and-non-local-referencing IBC mode.
 19. The method of claim18, wherein whether the loop filter process is enabled is derived fromthe at least one syntax element for signaling the IBC referencing mode.20. A video processing device for reconstructing a video block in avideo stream, comprising a memory for storing computer instructions anda processor for executing the computer instructions to: extract at leastone syntax element from the video stream, the at least one syntaxelement being associated with an intra block copy (IBC) prediction ofthe video block; determine an IBC referencing mode for the IBCprediction of the video block, the IBC referencing mode comprises one ofno-IBC mode, a local-referencing IBC mode, a non-local-referencing IBCmode, and a local-and-non-local-referencing IBC mode; and generatereconstructed samples of the video block from the video stream based onthe IBC referencing mode.